Plant root system morphology control agent

Abstract

The present invention provides a plant root system morphology control means which is effective and easy to use.　The present invention provides a plant root system morphology control agent comprising 2-aminopimelic acid or a salt or ester thereof.

Description

Plant root morphology regulator

[0001] The present invention relates to a plant root system morphology regulator comprising 2-aminopimelic acid or a salt or ester thereof. The present invention also relates to a plant root system morphology regulation method and a plant production method using 2-aminopimelic acid or a salt or ester thereof.

[0002] In plants, roots are essential organs for absorbing water and nutrients such as inorganic salts, fixing soil nutrients, and nitrogen metabolism. Plant root systems are broadly classified into taproot and fibrous root systems. Taproot systems are found in dicotyledonous plants and consist of a main root with a developed radicle and lateral roots growing from it. Taproot systems have a long, vertical taproot that supports the plant and is advantageous for absorbing water deep underground. On the other hand, fibrous root systems are found in monocotyledonous plants. They have little to no development of seminal roots, which correspond to the main root of taproot systems, and are primarily composed of nodal roots that grow in clusters at the nodes of the stem. Fibrous root systems are advantageous for growth in environments with abundant water and nutrients near the soil surface.

[0003] Since root system morphology can affect the efficiency of nutrient absorption from the roots and the growth of aboveground parts, it is important to develop techniques for controlling root system morphology.

[0004] Currently, root system morphology is mainly modified through breeding techniques using selective breeding, but this requires a huge amount of time and cost.

[0005] It is also known that external application of the plant hormone auxin inhibits taproot elongation and promotes lateral root growth (Non-Patent Document 1), but the strong effects of auxin limit its application. Furthermore, mepiquat chloride, a plant growth regulator used to increase cotton yields, is known to increase the number of lateral roots in cotton (Non-Patent Document 2), but its rooting effect is weak in Arabidopsis thaliana, limiting the plants to which it can be applied.

[0006] On the other hand, 2-aminopimelic acid is a non-proteinogenic amino acid with two carboxyl groups and one amino group, and has been reported to be present in plants of the Pteridophyceae family (Non-Patent Documents 3 and 4). However, its function has not yet been fully elucidated.

[0007] Ping Song et al., 2021, Planta, 254:69Xiaojiao Chen et al., 2018, BMC Plant Biology, 18:361Noriaki Murakami and Shin-ichi Hatanaka, 1983, Phytochemistry, Vol. 22, No. 12, pp. 2735-2737Noriaki Murakami et al., 1985, Phytochemistry, Vol. 24, No. 24, pp. 2291-2294

[0008] An object of the present invention is to provide an easy-to-use and effective means for controlling the root system morphology of plants.

[0009] To solve the above problems, the present inventors focused on 2-aminopimelic acid. They found that cultivating plants in a medium containing 2-aminopimelic acid inhibits taproot growth, increases lateral root density, and promotes root hair growth. They also demonstrated that rooting is promoted, leading to the completion of the present invention.

[0010] That is, the present invention encompasses the following: [1] A plant root system morphology regulator comprising 2-aminopimelic acid or a salt or ester thereof. [2] The root system morphology regulator according to [1], wherein the root system morphology is regulated by at least one selected from the group consisting of root hair formation, root hair growth promotion, and rooting promotion. [3] The root system morphology regulator according to [1] or [2], wherein the plant is a dicotyledonous plant. [4] A composition comprising the root system morphology regulator according to any one of [1] to [3]. [5] A method for regulating plant root system morphology, comprising the step of cultivating a plant in a medium containing 2-aminopimelic acid or a salt or ester thereof. [6] The method for regulating plant root system morphology according to [5], wherein the root system morphology is regulated by at least one selected from the group consisting of root hair formation, root hair growth promotion, and rooting promotion. [7] A plant production method, comprising the step of cultivating a plant in a medium containing 2-aminopimelic acid or a salt or ester thereof. [8] The method according to any one of [5] to [7], wherein the medium is a liquid medium. This specification includes the disclosure of Japanese Patent Application No. 2023-122555, from which the present application claims priority.

[0011] According to the present invention, the roots of a plant having a taproot-type root system can be changed to roots having a root system morphology similar to that of a fibrous root system.

[0012] 1 shows images of root morphology at seedling time of Arabidopsis thaliana cultivated for two weeks on MS medium without 2-aminopimelic acid (2-APA) (A) or on MS medium containing 2-APA (B). 2 shows graphs showing the primary root length (A) and lateral root density (B) of Arabidopsis thaliana cultivated for one or two weeks on MS medium without 2-aminopimelic acid (2-APA) or on MS medium containing 2-APA. 3 shows images of root hair morphology of Arabidopsis thaliana cultivated for two weeks on MS medium without 2-aminopimelic acid (2-APA) (A) or on MS medium containing 2-APA (B). 4 shows images of root morphology at seedling time of Arabidopsis ARF7 and ARF19-deficient mutants (arf7-1 arf19-1) cultivated on MS medium without 2-aminopimelic acid (2-APA) (A) or on MS medium containing 2-APA (B). Graphs showing the tap root length (A) and lateral root density (B) of radish grown for 12 days in SkyGel® water-retaining medium without 2-aminopimelic acid (2-APA) or in SkyGel water-retaining medium containing 2-APA (n=4). Graphs showing the tap root length (A) and lateral root density (B) of broccoli grown for 12 days in SkyGel water-retaining medium without 2-aminopimelic acid (2-APA) or in SkyGel water-retaining medium containing 2-APA (n=7). Graphs showing the tap root length (A) and lateral root density (B) of komatsuna (Japanese mustard spinach) grown for 12 days in SkyGel water-retaining medium without 2-aminopimelic acid (2-APA) or in SkyGel water-retaining medium containing 2-APA (n=5). Graphs showing the tap root length (A) and lateral root density (B) of garden cress grown for 12 days on SkyGel moist-retaining medium without 2-aminopimelic acid (2-APA) or with 2-APA (n=5). Graphs showing the tap root length (A) and lateral root density (B) of arugula grown for 12 days on SkyGel moist-retaining medium without 2-aminopimelic acid (2-APA) or with 2-APA (n=5). Graphs showing the tap root length (A) and lateral root density (B) of mustard grown for 12 days on SkyGel moist-retaining medium without 2-aminopimelic acid (2-APA) or with 2-APA (n=5).Graphs showing the tap root length (A) and lateral root density (B) of sunflowers grown for 12 days on SkyGel moist-retaining medium without 2-aminopimelic acid (2-APA) or with 2-APA (n=4). Graphs showing the tap root length (A) and lateral root density (B) of white sesame grown for 12 days on SkyGel moist-retaining medium without 2-aminopimelic acid (2-APA) or with 2-APA (n=2-4). Graphs showing the tap root length (A) and lateral root density (B) of red perilla grown for 12 days on SkyGel moist-retaining medium without 2-aminopimelic acid (2-APA) or with 2-APA (n=5). Graphs showing the tap root length (A) and lateral root density (B) of green perilla grown for 11 days in SkyGel moist-retaining medium without 2-aminopimelic acid (2-APA) or with 2-APA (n=5). Graphs showing the tap root length (A) and lateral root density (B) of red cabbage grown for 11 days in SkyGel moist-retaining medium without 2-aminopimelic acid (2-APA) or with 2-APA (n=5). Graphs showing the tap root length (A) and lateral root density (B) of alfalfa grown for 12 days in SkyGel moist-retaining medium without 2-aminopimelic acid (2-APA) or with 2-APA (n=5). This graph shows the tap root length (A) and lateral root density (B) of mungbean grown for 11 days on SkyGel wet-holding medium without 2-aminopimelic acid (2-APA) or with 2-APA (n=5). This graph shows the tap root length (A) and lateral root density (B) of swollen cabbage grown for 12 days on SkyGel wet-holding medium without 2-aminopimelic acid (2-APA) or with 2-APA (n=4-5). This graph shows the relative lateral root density of Arabidopsis thaliana grown on MS medium containing different concentrations of 2-aminopimelic acid (2-APA) or without 2-aminopimelic acid. Data are shown as mean ± standard deviation (n=7). 1 is an image showing the root morphology of Komatsuna grown hydroponically in a Hyponex solution containing no 2-aminopimelic acid (2-APA) or a Hyponex solution containing 2-APA.(A) Root morphology (arrow) of komatsuna grown hydroponically in a Hyponex solution without 2-aminopimelic acid on the 12th day after sowing. (B) Root morphology (arrow) of komatsuna grown hydroponically in a Hyponex solution with 2-aminopimelic acid on the 12th day after sowing. (C) Root morphology (arrow) of komatsuna grown hydroponically in a Hyponex solution without 2-aminopimelic acid on the 24th day after sowing. (D) Root morphology (arrow) of komatsuna grown hydroponically in a Hyponex solution with 2-aminopimelic acid on the 24th day after sowing. This figure shows (A) the aboveground fresh weight and (B) the aboveground fresh weight / root organ fresh weight of komatsuna grown hydroponically for approximately one month in a Hyponex solution without 2-aminopimelic acid (2-APA) or with 2-APA (40 days after sowing, n=5). 1 shows images of root morphology at the time of seedling emergence of Arabidopsis thaliana grown for two weeks on MS medium containing no 2-aminopimelic acid (2-APA) (A), MS medium containing DL-2-APA (B), or MS medium containing L-2-APA (C). 1 shows graphs showing the primary root length (A) and lateral root density (B) of Arabidopsis thaliana grown for two weeks on MS medium containing no 2-aminopimelic acid (2-APA), MS medium containing DL-2-APA, or MS medium containing L-2-APA.

[0013] The present invention will be described in detail below.

[0014] The present invention relates to the use of 2-aminopimelic acid or a salt or ester thereof for regulating the root morphology of plants. In particular, the present invention relates to the use of 2-aminopimelic acid or a salt or ester thereof for inducing root hair formation, promoting root hair growth, and promoting root formation in plants.

[0015] (1) Root System Morphology Regulator The present invention provides a plant root system morphology regulator.

[0016] As used herein, "control of root system morphology" means changing the root system morphology to a desired morphology. The control of root system morphology is particularly at least one selected from the formation of root hairs, promotion of root hair growth, and promotion of root development. The control of root system morphology may be, for example, the formation of root hairs and promotion of root hair growth, or the formation of root hairs and promotion of root development, or the formation of root hairs, promotion of root hair growth, and promotion of root development.

[0017] As used herein, "fiber rooting" refers to a change in the root system morphology of a plant to a fiber-type root system morphology or a similar morphology, particularly to the suppression of taproot growth and an increase in lateral root density. As used herein, "suppressing taproot growth" encompasses shortening the taproot length and suppressing taproot elongation. As used herein, "lateral root density" refers to the number of lateral roots (particularly the number of primary lateral roots) per unit length arising from the taproot, and can be calculated by dividing the taproot length by the number of lateral roots.

[0018] As used herein, "promoting root hair growth" means increasing the number and / or length of root hairs. As used herein, "root hair" refers to a hair-like organ that grows from a part of the root epidermis. Root hairs increase the surface area of ​​the root, thereby improving the efficiency of water and nutrient absorption, and also serve to anchor the root to the soil.

[0019] As used herein, "promoting root formation" means promoting root formation, particularly increasing the number of lateral roots.

[0020] As used herein, the term "root system morphology regulator" refers to a drug comprising 2-aminopimelic acid or a salt or ester thereof, preferably 2-aminopimelic acid or a salt thereof, which has the effect of regulating plant root system morphology.

[0021] As shown in the Examples below, 2-aminopimelic acid inhibits taproot growth and increases lateral root density (i.e., induces plant hair root formation). 2-aminopimelic acid also promotes root hair growth and increases the number of lateral roots. Therefore, 2-aminopimelic acid and its analogs, salts and esters of 2-aminopimelic acid, can be used as active ingredients in the root system morphology regulator of the present invention.

[0022] 2-aminopimelic acid is a compound represented by the following formula (I):

[0023] 2-aminopimelic acid may be in the D-form, the L-form, or an equal mixture thereof (DL-form), but is preferably in the L-form or DL-form, more preferably in the L-form.

[0024] The salt of 2-aminopimelic acid is not particularly limited as long as it is an agriculturally acceptable salt, and examples thereof include acid addition salts, metal salts, ammonium salts, amine salts, etc. Examples of acid addition salts include hydrochloride, phosphate, nitrate, sulfate, acetate, propionate, butyrate, valerate, citrate, fumarate, maleate, malate, etc. Examples of metal salts include alkaline earth metal salts such as magnesium salt and calcium salt, aluminum salt, and zinc salt.

[0025] The ester of 2-aminopimelic acid is not particularly limited as long as it is an agriculturally acceptable ester, and may be, for example, an ester in which one or both hydrogen atoms of the two carboxyl groups contained in 2-aminopimelic acid are substituted with an alkyl group. Examples of the alkyl group include C1 to C5 alkyl groups (linear or branched alkyl groups having 1 to 5 carbon atoms), such as a methyl group (-CH3), an ethyl group (-C2H5), a propyl group (-C3H7), a butyl group (-C4H9), and a pentyl group (-C5H 11 ) are listed.

[0026] Commercially available 2-aminopimelic acid may be used, and can be obtained, for example, from Fujifilm Wako Pure Chemical Industries, Ltd. and Tokyo Chemical Industry Co., Ltd. Salts or esters of 2-aminopimelic acid can be obtained from 2-aminopimelic acid by a conventional method. 2-aminopimelic acid or its salts or esters may be isolated or purified.

[0027] The target plants of the root system morphology regulator of the present invention may be any plants including angiosperms (dicotyledons and monocotyledons), gymnosperms, ferns, bryophytes, and algae, but are preferably plants with a taproot-type root system, such as dicotyledons. The plants may be ornamental flowering plants or agricultural crops such as edible vegetables and fruits. Examples of dicotyledons include Brassicaceae (e.g., Arabidopsis thaliana, radish, broccoli, komatsuna, cress, arugula, mustard greens, cabbage, Chinese cabbage, mizuna, bok choy, etc.), Asteraceae (e.g., chrysanthemum, sunflower, lettuce, etc.), Pedaliaceae (e.g., sesame, etc.), Lamiaceae (e.g., perilla, sage, thyme, basil, mint, lavender, lemon balm, rosemary, etc.), and Leguminosae (e.g., alfalfa, rye, etc.). Examples of suitable plants include those from the following families: rice bran, adzuki bean, kidney bean, broad bean, pea, soybean, chickpea, peanut, etc.), Convolvulaceae (e.g., watercress, sweet potato, etc.), Cucurbitaceae (e.g., cucumber, pumpkin, watermelon, melon, zucchini, etc.), Rosaceae (e.g., strawberry, peach, pear, apple, almond, etc.), Apiaceae (e.g., carrot, celery, parsley, etc.), and Solanaceae (e.g., eggplant, tomato, potato, bell pepper, etc.).The target plant is preferably, but not limited to, Arabidopsis (Arabidopsis thaliana), radish (Raphanus sativus var. Longipinnatus), broccoli (Brassica oleracea var. italica), komatsuna (Brassica rapa var. perviridis), garden cress (Lepidium sativum), arugula (Eruca vesicaria), mustard (Brassica juncea), sunflower (Helianthus annuus), white sesame (Sesamum indicum), red shiso (Perilla frutescens var. crispa f. purpurea), green shiso (Perilla frutescens var. crispa f. viridis), red cabbage (Brassica oleracea var. capitata), alfalfa (Medicago sativa), mung bean (Vigna radiata), or swamp cabbage (Ipomoea aquatica).

[0028] Whether 2-aminopimelic acid or its salts or esters have the ability to induce fibrous root formation in plants can be evaluated by comparing the taproot length and lateral root density of plants grown in a medium containing 2-aminopimelic acid or its salts or esters with those grown in a medium not containing 2-aminopimelic acid or its salts or esters. For example, plant seeds are sown in a medium containing 2-aminopimelic acid or its salts or esters, or in a medium not containing 2-aminopimelic acid or its salts or esters, and grown for a predetermined period (e.g., two weeks), after which the taproot length and the number of lateral roots (particularly the number of primary lateral roots) of the resulting plants are measured. If the average taproot length of plants grown in a medium containing 2-aminopimelic acid or its salts or esters is reduced by 10% or more and the average lateral root density is increased by 10% or more compared to plants grown in a medium not containing 2-aminopimelic acid or its salts or esters, it can be determined that 2-aminopimelic acid or its salts or esters has the ability to induce fibrous root formation in plants.

[0029] Whether 2-aminopimelic acid or a salt or ester thereof has the effect of promoting root hair growth can be evaluated by comparing the number and / or length of root hairs of plants grown in a medium containing 2-aminopimelic acid or a salt or ester thereof with those grown in a medium not containing 2-aminopimelic acid or a salt or ester thereof. For example, plant seeds are sown in a medium containing 2-aminopimelic acid or a salt or ester thereof, or in a medium not containing 2-aminopimelic acid or a salt or ester thereof, and grown for a predetermined period (e.g., 2 weeks). If the average number and / or length of root hairs in plants grown in a medium containing 2-aminopimelic acid or a salt or ester thereof is increased by 10% or more compared to plants grown in a medium not containing 2-aminopimelic acid or a salt or ester thereof, it can be determined that 2-aminopimelic acid or a salt or ester thereof has the effect of promoting root hair growth.

[0030] Whether 2-aminopimelic acid or its salts or esters has a root-promoting effect can be evaluated by comparing the number of lateral roots (particularly the number of primary lateral roots) of plants grown in a medium containing 2-aminopimelic acid or its salts or esters with that grown in a medium not containing 2-aminopimelic acid or its salts or esters. For example, plant seeds are sown in a medium containing 2-aminopimelic acid or its salts or esters, or in a medium not containing 2-aminopimelic acid or its salts or esters, and grown for a predetermined period (e.g., two weeks), and the number of lateral roots of the resulting plants is measured. 2-aminopimelic acid or its salts or esters can be determined to have a root-promoting effect if the average number of lateral roots in plants grown in a medium containing 2-aminopimelic acid or its salts or esters is increased by 10% or more compared to plants grown in a medium not containing 2-aminopimelic acid or its salts or esters.

[0031] The root system morphology regulator of the present invention can dwarf the rhizosphere and reduce the total root weight by suppressing the growth of the taproot, while at the same time increasing the efficiency of nutrient absorption from the roots by changing the root system morphology. As a result, the root system morphology regulator of the present invention can dwarf the rhizosphere and reduce the total root weight while maintaining the growth of the above-ground part, which leads to saving the amount of soil or water used for plant cultivation and ultimately saving cultivation space. Therefore, the root system morphology regulator of the present invention is particularly useful for nutrient culture such as hydroponics, where saving the amount of soil or water used for cultivation and cultivation space are important.

[0032] The root system morphology regulator of the present invention can also be used, for example, to promote rooting of cuttings or seedlings. Since the root system morphology regulator of the present invention has a root hair growth-promoting effect and a root-promoting effect, it can also be used, for example, to promote the establishment of plants after transplanting.

[0033] Currently, commercially available rooting agents that promote rooting include "hormone-type rooting agents" that use auxins as active ingredients, and "activator-type rooting agents" that use vitamins and minerals as active ingredients to promote rooting by improving nutritional status (https: / / www.sc-engei.co.jp / guide / detail / 1421, https: / / www.sun-g-orient.co.jp / hakkonryoku / ). However, hormone-type rooting agents have issues such as concerns about their environmental impact due to the use of high concentrations of plant hormones, and their extremely strong effects limit their use to soaking for a few days. Furthermore, because the nutritional requirements of activate-type rooting agents vary depending on the cultivation environment and plant variety, it is difficult to optimize their functional efficiency as rooting agents.

[0034] Because the root system morphology regulator of the present invention is not a plant hormone, there are no limitations on its usage, unlike hormone-type rooting agents that use auxins as active ingredients. The root system morphology regulator of the present invention can be used more easily than hormone-type rooting agents, simply by adding it to the medium in which the plant is grown. Furthermore, as shown in the examples below, the mechanism of action of the root system morphology regulator of the present invention is thought to be similar to that of hormone-type rooting agents, and therefore the root system morphology regulator of the present invention can promote plant rooting more directly than active-type rooting agents that use vitamins, minerals, etc. as active ingredients.

[0035] In one embodiment, the root system morphology regulator of the present invention is a root fibrous regulator for dicotyledonous plants, such as plants of the Brassicaceae, Asteraceae, Pedaliaceae, Lamiaceae, Fabaceae, or Convolvulaceae families.

[0036] In one embodiment, the root system morphology regulator of the present invention may be a root hair growth promoter for Brassicaceae plants.

[0037] In one embodiment, the root system morphology regulator of the present invention may be a root promoter for Asteraceae or Brassicaceae plants, such as sunflower or cabbage.

[0038] (2) Composition The present invention provides a composition containing 2-aminopimelic acid or a salt or ester thereof, or the root system morphology regulator of the present invention (hereinafter also referred to as the "composition of the present invention"). The composition of the present invention can be used for controlling plant root system morphology, particularly for at least one selected from the formation of plant hair roots, promotion of root hair growth, and promotion of root development.

[0039] The composition of the present invention comprises 2-aminopimelic acid or a salt or ester thereof, preferably 2-aminopimelic acid or a salt thereof, as an essential active ingredient.

[0040] The compositions of the present invention may further contain other plant growth regulators or essential elements, such as hydrogen (H), oxygen (O), carbon (C), nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca), sulfur (S), iron (Fe), manganese (Mg), zinc (Zn), boron (B), molybdenum (Mo), copper (Cu), chlorine (Cl), and nickel (Ni).

[0041] In addition to the above-mentioned components, the composition of the present invention may further contain agriculturally acceptable additives (for example, carriers (such as solid or liquid carriers), excipients, diluents, disintegrants, binders, coating agents, lubricants, glidants, gliding agents, emulsifiers, surfactants, solubilizers, suspending agents, preservatives, buffers, pH adjusters), etc.

[0042] The composition of the present invention may be formulated into any dosage form, such as solid preparations such as dusts, granules, powders, wettable powders, and water-soluble powders; liquid preparations such as emulsifiable concentrates, solutions, and oil solutions; aerosols, pastes, and sprays. The composition of the present invention may be, for example, a solution in which 2-aminopimelic acid or a salt or ester thereof is dissolved in an appropriate solution. Examples of the appropriate solution include water (including sterilized water, deionized water, and ultrapure water), buffer solutions, and liquid media.

[0043] The composition of the present invention can be used, for example, by adding it to a medium for growing plants. The content of 2-aminopimelic acid or a salt or ester thereof in the composition of the present invention is not limited, as long as the final concentration of 2-aminopimelic acid or a salt or ester thereof when added to a medium or the like is a concentration that is effective for controlling plant root morphology (such as root hair formation, promoting root hair growth, or promoting root formation). The concentration of 2-aminopimelic acid or a salt or ester thereof in the composition of the present invention is not limited, and can be, for example, 0.1 μM or more, 1 μM or more, 10 μM or more, 50 μM or more, 100 μM or more, 1 mM or more, or 10 mM or more, 1 M or less, 500 mM or less, 100 mM or less, or 50 mM or less, for example, 10 μM to 100 mM, 50 μM to 100 mM, 100 μM to 100 mM, 1 mM to 100 mM, 10 mM to 100 mM, 10 μM to 50 mM, 50 μM to 50 mM, 100 μM to 50 mM, 1 mM to 50 mM, or 10 mM to 50 mM. The composition of the present invention can be added to a culture medium so that the concentration of 2-aminopimelic acid or a salt or ester thereof in the culture medium is, for example, 0.1 μM or more, 1 μM or more, 10 μM or more, 50 μM or more, 60 μM or more, 70 μM or more, 80 μM or more, or 90 μM or more, 10 mM or less, 1 mM or less, 500 μM or less, 400 μM or less, 300 μM or less, 200 μM or less, 150 μM or less, 140 μM or less, 130 μM or less, 120 μM or less, or 110 μM or less, for example, 0.1 μM to 10 mM, 1 μM to 1 mM, 50 μM to 500 μM, 50 μM to 150 μM, or 90 μM to 110 μM.

[0044] The subjects to which the composition of the present invention is administered are the same as those to which the root system morphology regulator of the present invention is administered, and include, for example, angiosperms (dicotyledons and monocotyledons), gymnosperms, ferns, bryophytes, algae, preferably dicotyledons, more preferably plants of the Brassicaceae, Asteraceae, Pedaliaceae, Lamiaceae, Fabaceae, Convolvulaceae, Cucurbitaceae, Rosaceae, Apiaceae, or Solanaceae families, and even more preferably Arabidopsis thaliana, radish, broccoli, komatsuna, cress, arugula, mustard, sunflower, white sesame, red perilla, green perilla, red cabbage, alfalfa, mung bean, or swiss cabbage.

[0045] (3) Method for controlling root system morphology The present invention relates to a method for controlling plant root system morphology (sometimes referred to as the "method for controlling root system morphology of the present invention"), which comprises a step of cultivating a plant in a medium containing 2-aminopimelic acid or a salt or ester thereof, or the root system morphology regulator of the present invention. In the method for controlling root system morphology of the present invention, the control of root system morphology can be, for example, at least one selected from the group consisting of root hair formation, promotion of root hair growth, and promotion of rooting.

[0046] As used herein, the term "culture medium" refers to a medium used for plant cultivation and encompasses both liquid and solid media. Liquid media are not particularly limited as long as they are suitable for plant cultivation, but preferably contain essential elements (e.g., hydrogen (H), oxygen (O), carbon (C), nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca), sulfur (S), iron (Fe), manganese (Mg), zinc (Zn), boron (B), molybdenum (Mo), copper (Cu), chlorine (Cl), and nickel (Ni)). Liquid media may contain, for example, inorganic salts (e.g., potassium nitrate, ammonium nitrate, magnesium sulfate, ferrous sulfate, manganese sulfate, zinc sulfate, copper sulfate, potassium phosphate, sodium molybdate, ethylenediaminetetraacetic acid disodium salt, boric acid, calcium chloride, cobalt chloride, potassium iodide, etc.), sugars, amino acids, vitamins, etc. Examples of liquid media that can be used include Murashige-Skoog (MS) medium, White's medium, and commercially available Hyponex® solution. Examples of solid media include culture soil, liquid media solidified by adding a gelling agent such as agar, gelatin, gellan gum, cross-linked polyacrylic acid polymer, gravel, sand, vermiculite, perlite, rock wool, rice husks, bark, peat moss, coconut shells, polyester, urethane, etc. A solid medium may be used by adding a liquid medium.

[0047] 2-Aminopimelic acid or a salt or ester thereof may be added to the medium in an amount effective for controlling the root system morphology of a plant (inducing root hair formation, promoting root hair growth, promoting root formation, etc.). For example, 2-aminopimelic acid or a salt or ester thereof can be added to the medium so that the concentration in the medium is 0.1 μM or more, 1 μM or more, 10 μM or more, 50 μM or more, 60 μM or more, 70 μM or more, 80 μM or more, or 90 μM or more, 10 mM or less, 1 mM or less, 500 μM or less, 400 μM or less, 300 μM or less, 200 μM or less, 150 μM or less, 140 μM or less, 130 μM or less, 120 μM or less, or 110 μM or less, for example, 0.1 μM to 10 mM, 1 μM to 1 mM, 50 μM to 500 μM, 50 μM to 150 μM, or 90 μM to 110 μM.

[0048] Plants cultivated using the root system morphology control method of the present invention are similar to the targets of administration of the root system morphology regulator of the present invention described above, and include, for example, angiosperms (dicotyledons and monocotyledons), gymnosperms, ferns, bryophytes, algae, preferably dicotyledons, more preferably plants of the Brassicaceae, Asteraceae, Pedaliaceae, Lamiaceae, Fabaceae, Convolvulaceae, Cucurbitaceae, Rosaceae, Apiaceae, or Solanaceae families, and even more preferably Arabidopsis thaliana, radish, broccoli, komatsuna, cress, arugula, mustard greens, sunflower, white sesame, red perilla, green perilla, red cabbage, alfalfa, mung bean, or swiss cabbage. As used herein, "plant" includes the whole plant, parts thereof, seeds, etc., unless otherwise indicated by the context. Examples of plant parts include leaves, stems, roots, shoot tips, axillary buds, ovaries, embryos, pollen, anthers, tissue fragments containing these, and cultured cells (for example, callus).

[0049] In the method for controlling root system morphology of the present invention, cultivation in a medium containing 2-aminopimelic acid or a salt or ester thereof may be carried out at any appropriate timing, for example, during seedling raising, after planting of the seedlings, or during the period from sowing to harvesting of the plants.

[0050] In the method for controlling root system morphology of the present invention, the cultivation form is not particularly limited, and may be, for example, soil cultivation, nutrient solution soil cultivation, or nutrient solution cultivation (including hydroponics, rock wool cultivation, coco peat cultivation, etc.).

[0051] Cultivation conditions may be appropriately determined depending on the type of plant, and the cultivation temperature can be, for example, 15°C to 30°C, 20°C to 30°C, or 20°C to 25°C. The light / dark cycle can be, for example, 6 to 18 hours, 10 to 18 hours, 14 to 18 hours, or 16 hours of light and 6 to 18 hours, 6 to 14 hours, 6 to 10 hours, or 8 hours of dark. The cultivation period can be, for example, 1 day or more, 3 days or more, 1 week or more, or 2 weeks or more, 1 year or less, 6 months or less, 3 months or less, 1 month or less, 4 weeks or less, or 3 weeks or less, such as 1 week to 1 year, 1 week to 6 months, 1 week to 3 months, 1 week to 1 month, 1 week to 3 weeks, 2 weeks to 1 year, 2 weeks to 6 months, 2 weeks to 3 months, 2 weeks to 1 month, or 2 weeks to 3 weeks. When cultivating komatsuna hydroponically, the cultivation temperature should be 20 to 25°C, the photoperiod should be approximately 16 hours of light and 8 hours of darkness, and the cultivation period should be 2 weeks to 1 month.

[0052] In one embodiment, the cultivation step may include a step of sowing plant seeds in a medium containing 2-aminopimelic acid or a salt or ester thereof and raising the seedlings, and a step of planting the obtained seedlings in another medium containing 2-aminopimelic acid or a salt or ester thereof and cultivating them.

[0053] (4) Plant Production Method The present invention relates to a plant production method (sometimes referred to as the "production method of the present invention"), which comprises a step of cultivating a plant in a medium containing 2-aminopimelic acid or a salt or ester thereof.

[0054] In the production method of the present invention, the step of cultivating in a medium containing 2-aminopimelic acid or a salt or ester thereof is the same as in the method of controlling root system morphology of the present invention.

[0055] In the production method of the present invention, by cultivating a plant in a medium containing 2-aminopimelic acid or a salt or ester thereof, the root morphology of the plant can be controlled, and in particular, at least one effect selected from the group consisting of root hair formation, promotion of root hair growth, and promotion of root formation can be achieved.

[0056] The production method of the present invention may or may not further include a step of cultivating a plant in a medium that does not contain 2-aminopimelic acid or a salt or ester thereof.

[0057] According to the production method of the present invention, the root system of a plant can be made fibrous by the action of 2-aminopimelic acid or a salt or ester thereof, and the efficiency of plant cultivation can be improved in environments where fibrous root systems are more advantageous for growth than taproot systems (e.g., environments with abundant moisture and nutrients near the ground surface).For example, in hydroponic cultivation, the amount of soil or water used for cultivation and the cultivation space can be saved.

[0058] The present invention will be described in more detail below using examples, although the technical scope of the present invention is not limited to these examples.

[0059] Example 1: Effect of 2-aminopimelic acid on root morphology of Arabidopsis thaliana The following experiment was carried out to examine the effect of 2-aminopimelic acid on root morphology of Arabidopsis thaliana.

[0060] Murashige and Skoog (MS) medium was prepared by dissolving Murashige and Skoog Plant Salt Mixture (Fujifilm Wako Pure Chemical Corporation) in distilled water, adding 0.1% MES (Nacalai Tesque, Inc.) and 0.2–0.4% Gellan Gum (Fujifilm Wako Pure Chemical Corporation), and dry-heat sterilization. DL-2-aminopimelic acid (CAS RN: 627-76-9, Tokyo Chemical Industry Co., Ltd.) was added to the dry-heat sterilized MS medium to prepare MS medium containing 2-aminopimelic acid at a final concentration of 100 μM.

[0061] Seeds of the wild-type Arabidopsis thaliana strain Columbia-0 (Col-0) were surface-sterilized and sown on MS medium containing 100 μM 2-aminopimelic acid in a square Petri dish (Eiken Chemical Co., Ltd.). As a control, sterilized seeds were sown on MS medium without 2-aminopimelic acid.

[0062] The plants were exposed to low temperatures for three days, including the day of sowing, at 4°C in the dark. They were then cultivated at 22°C under a 16-hour light / 8-hour dark photoperiod. One and two weeks later, the length of the main root of the plants was measured with a vernier caliper, and the number of lateral roots (primary lateral roots) was counted. The lateral root density was calculated by dividing the number of lateral roots by the main root length.

[0063] The results are shown in Figures 1 to 3. On MS medium containing 2-aminopimelic acid, the primary root length decreased, while the lateral root density increased, compared to MS medium without 2-aminopimelic acid (Figures 1 and 2). These results indicate that cultivation in the presence of 2-aminopimelic acid changes the roots of a primary root system to a form similar to that of a fibrous root system, i.e., fibrous root formation. Furthermore, on MS medium containing 2-aminopimelic acid, the number and length of root hairs increased compared to MS medium without 2-aminopimelic acid (Figure 3). These results indicate that 2-aminopimelic acid promotes root hair growth.

[0064] Example 2: Effect of 2-aminopimelic acid on root morphology of ARF7 and ARF19-deficient mutants of Arabidopsis thaliana The changes in root morphology of Arabidopsis thaliana observed in the presence of 2-aminopimelic acid in Example 1 were similar to the changes in root morphology of Arabidopsis thaliana observed in the presence of the plant hormone auxin (Ping Song et al., 2021, Planta, 254:69, pp. 1-13).

[0065] Therefore, we conducted the following experiment to examine the relationship between 2-aminopimelic acid and auxin biosynthesis using Arabidopsis thaliana lacking the auxin response genes ARF7 and ARF19 (arf7-1 arf19-1; Arabidopsis Biological Resource Center).

[0066] Surface-sterilized seeds of the arf7-1 arf19-1 strain were sown on MS medium containing or not containing 100 μM 2-aminopimelic acid, subjected to low-temperature treatment, and cultivated for 2 weeks, after which the root morphology was observed. The medium, sowing, low-temperature treatment, and cultivation method used were as described in Example 1.

[0067] The results are shown in Figure 4. 2-aminopimelic acid did not affect root morphology in the arf7-1 arf19-1 plants. This result suggests that 2-aminopimelic acid alters root morphology by regulating auxin biosynthesis or action.

[0068] Example 3: Effects of 2-aminopimelic acid on root morphology of various plants The following experiment was carried out to investigate the effects of 2-aminopimelic acid on the root morphology of various plants other than Arabidopsis thaliana.

[0069] A suitable amount of SkyGel (registered trademark) (Maybiol Corporation) and 100 ml of RO water were added to a plant box (AS ONE) to prepare a SkyGel-containing medium. A suitable amount of SkyGel and 100 ml of a 100 μM DL-2-aminopimelic acid (CAS RN: 627-76-9, Tokyo Chemical Industry Co., Ltd.) solution were also added to the plant box to prepare a SkyGel-containing medium containing 100 μM 2-aminopimelic acid.

[0070] Brassicaceae plants include radish (Raphanus sativus var. Longipinnatus), broccoli (Brassica oleracea var. italica), komatsuna (Brassica rapa var. perviridis), garden cress (Lepidium sativum), arugula (Eruca vesicaria), mustard (Brassica juncea), and red cabbage (Brassica oleracea var. capitata); Asteraceae plants include sunflower (Helianthus annuus); Sesamum indicum; Lamiaceae plants include red perilla (Perilla frutescens var. crispa f. purpurea) and green perilla (Perilla frutescens var. crispa f. viridis); and legumes include alfalfa (Medicago sativa) and mung bean (Vigna Seeds (Nakahara Seed Co., Ltd.) of the Convolvulaceae family, Ipomoea aquatica (Panax radiata), and Ipomoea aquatica (Panax radiata) were disinfected for several seconds with 80% ethanol and then sown on SkyGel moistening medium containing 100 μM 2-aminopimelic acid. Control seeds were also sown on SkyGel moistening medium without 2-aminopimelic acid. The plants were then grown at 23°C under a 16-hour light / 8-hour dark photoperiod. After two weeks, the taproot length of the plants was measured with a vernier caliper, and the number of lateral roots (primary lateral roots) was also measured. The lateral root density was calculated by dividing the number of lateral roots by the taproot length.

[0071] The results are shown in Figures 5 to 18 and Table 1 below. For all tested plants, when grown on SkyGel moist medium containing 2-aminopimelic acid, the tap root length decreased and the lateral root density increased compared to when grown on SkyGel moist medium without 2-aminopimelic acid. These results demonstrate that the root-forming effect of 2-aminopimelic acid is effective not only for Arabidopsis thaliana, but also for dicotyledonous plants of various other families.

[0072]

[0073] In addition, 2-aminopimelic acid significantly increased the number of lateral roots in sunflower and red cabbage. When sunflower was grown on SkyGel medium containing or without 2-aminopimelic acid, the average number of lateral roots was 50 and 61.5, respectively. When red cabbage was grown on SkyGel medium containing or without 2-aminopimelic acid, the average number of lateral roots was 14.4 and 27.6, respectively. These results indicate that 2-aminopimelic acid can promote root formation.

[0074] Example 4: Effects of various concentrations of 2-aminopimelic acid on root morphology The following experiment was carried out to investigate the effects of various concentrations of 2-aminopimelic acid on root morphology.

[0075] According to the method described in Example 1, MS media containing 2-aminopimelic acid at final concentrations of 1 μM, 10 μM, or 100 μM were prepared.

[0076] Arabidopsis thaliana (Columbia-0) seeds were sterilized and sown on MS medium containing 2-aminopimelic acid in a square Petri dish by the method described in Example 1. As a control, sterilized Arabidopsis thaliana seeds were sown on MS medium not containing 2-aminopimelic acid.

[0077] After sowing, the plants were cultivated at 23°C under a 16-hour light / 8-hour dark photoperiod. After two weeks, the taproot length of the plants was measured with a vernier caliper, and the number of lateral roots (number of primary lateral roots) was also measured. The number of lateral roots was divided by the taproot length to calculate the lateral root density. The relative lateral root density was calculated by dividing the lateral root density of plants cultivated on MS medium containing 2-aminopimelic acid by the lateral root density of plants cultivated on MS medium without 2-aminopimelic acid, which was set at 100%.

[0078] The results are shown in Figure 19. The lateral root density increased depending on the concentration of 2-aminopimelic acid.

[0079] Example 5: Effect of 2-aminopimelic acid in hydroponic cultivation The following experiment was carried out to confirm the effect of 2-aminopimelic acid in hydroponic cultivation.

[0080] According to the method described in Example 3, a 2-aminopimelic acid-free SkyGel hydrated medium and a 100 μM 2-aminopimelic acid-containing SkyGel hydrated medium were prepared.

[0081] Komatsuna seeds (Nakahara Seed Co., Ltd.) were sown in SkyGel moist medium without 2-aminopimelic acid or in SkyGel moist medium containing 100 μM 2-aminopimelic acid, and cultivated for approximately one week under conditions of a temperature of 23°C and a photoperiod of 16 hours light and 8 hours dark.

[0082] The resulting seedlings were transplanted into a hydroponic cultivation kit (Home Hyponica Pukupuku II, Kyowa Co., Ltd.) and grown in a hydroponic environment. The hydroponic solution used was either a 0.5 g / L Hyponex solution (Hyponex Japan Co., Ltd.) or a 0.5 g / L Hyponex solution containing DL-2-aminopimelic acid (CAS RN: 627-76-9, Tokyo Chemical Industry Co., Ltd.) dissolved at a final concentration of 100 μM. Approximately one month after the start of cultivation, the fresh weight of the aboveground parts and root organs of the plants was measured using an electronic balance (Shimadzu).

[0083] The root morphology of komatsuna plants 12 and 24 days after sowing is shown in Figure 20. Compared to komatsuna plants grown in the absence of 2-aminopimelic acid, komatsuna plants grown in the presence of 2-aminopimelic acid had shorter taproots, increased lateral root density, and smaller rhizospheres. The average taproot length of komatsuna plants grown in the absence or presence of 2-aminopimelic acid on the 12th day after sowing was 7.58 cm and 3.29 cm, respectively. The average lateral root density of komatsuna plants grown in the absence or presence of 2-aminopimelic acid on the 12th day after sowing was 3.12 / cm and 6.09 / cm, respectively.

[0084] The results of measuring the fresh weight of the aboveground parts and the fresh weight of the root organs of the plants are shown in Figure 21. Compared to komatsuna plants grown in the absence of 2-aminopimelic acid, the fresh weight of the root organs in komatsuna plants grown in the presence of 2-aminopimelic acid was reduced, but the fresh weight of the aboveground parts was slightly increased. A two-tailed Student's t-test showed a significant increase in the ratio of aboveground part fresh weight to root organ fresh weight. The increase in aboveground growth despite the decrease in total root mass is thought to be due to an increase in nutrient absorption efficiency due to changes in root system morphology.

[0085] The dwarfing of the rhizosphere and the reduction in the total root mass lead to a reduction in the amount of soil or water required for cultivation. Therefore, the above results indicate that cultivation in the presence of 2-aminopimelic acid can reduce the amount of soil or water required for cultivation without adversely affecting the growth of aboveground parts.

[0086] Example 6: Effect of L-2-aminopimelic acid on root morphology The following experiment was carried out to compare the effect of DL-2-aminopimelic acid and L-2-aminopimelic acid on root morphology.

[0087] An MS medium containing 100 μM DL-2-aminopimelic acid and an MS medium not containing 2-aminopimelic acid were prepared as described in Example 1. In addition, an MS medium containing 100 μM L-2-aminopimelic acid was prepared in the same manner as described in Example 1, except that L-2-aminopimelic acid was used instead of DL-2-aminopimelic acid.

[0088] Surface-sterilized seeds of Arabidopsis thaliana Columbia-0 (Col-0) were sown on MS medium containing DL-2-aminopimelic acid, MS medium containing L-2-aminopimelic acid, or MS medium not containing 2-aminopimelic acid, subjected to low-temperature treatment, and cultivated for 2 weeks, after which the taproot length and lateral root density were measured. The sowing, low-temperature treatment, cultivation methods, and methods for measuring the taproot length and lateral root density were as described in Example 1.

[0089] The results are shown in Figures 22 and 23. Both DL-2-aminopimelic acid and L-2-aminopimelic acid reduced taproot length and increased lateral root density, resulting in the formation of fibrous roots in the taproot-type root system, with L-2-aminopimelic acid showing a stronger fibrous root formation effect than DL-2-aminopimelic acid. All publications, patents, and patent applications cited herein are incorporated herein by reference in their entirety.

Claims

1. A plant root morphology regulator comprising 2-aminopimelic acid or a salt or ester thereof.

2. The root system morphology regulator according to claim 1, wherein the control of root system morphology is at least one selected from the formation of root hairs, promotion of root hair growth, and promotion of rooting.

3. A root system morphology regulator according to claim 1 or 2, wherein the plant is a dicotyledonous plant.

4. A composition comprising the root system morphology regulator according to claim 1.

5. A method for controlling the root morphology of a plant, comprising a step of cultivating a plant in a medium containing 2-aminopimelic acid or a salt or ester thereof.

6. The method for controlling plant root system morphology according to claim 5, wherein the control of root system morphology is at least one selected from the formation of root hairs, promotion of root hair growth, and promotion of rooting.

7. A method for producing a plant, comprising the step of cultivating a plant in a medium containing 2-aminopimelic acid or a salt or ester thereof.

8. The method according to any one of claims 5 to 7, wherein the medium is a liquid medium.

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