Application of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in regulating and controlling thickness of secondary cell wall of plant

Abstract

The invention relates to the technical field of gene engineering, in particular to application of a mitochondrial GPAT1 gene and a mitochondrial GPAT2 gene in regulating and controlling the thickness of a plant secondary cell wall. The invention discovers that the mitochondrial GPAT1 gene and the mitochondrial GPAT2 gene have the effect of regulating and controlling the thickness of the secondary cell wall of the plant for the first time, which is specifically embodied in that the mitochondrial GPAT1 gene and the mitochondrial GPAT2 gene regulate the formation of the secondary cell wall through negative regulation and control of lignin and cellulose biosynthesis related genes. Results of the specific embodiment of the invention show that when the mitochondrial GPAT1 gene and the mitochondrial GPAT2 gene are deleted, lignin and cellulose synthetic genes are up-regulated, a large amount of lignin and cellulose are accumulated in cell walls of arabidopsis thaliana double mutant gpat1 and gpat2 seedlings, the cell walls become thicker and harder, and cotyledons are harder in texture.

Description

Technical Field

[0001] The invention relates to the technical field of genetic engineering, and in particular to the application of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in regulating the thickness of plant secondary cell walls. Background Art

[0002] The secondary cell wall (SCW) is located between the primary cell wall and the plasma membrane and is composed of lignin, cellulose, and hemicellulose (Wang et al. 2023). The biosynthesis of lignin in plants begins with the phenylpropanoid metabolic pathway. Lignin is a natural complex macromolecular phenolic polymer located between cellulose and hemicellulose in the cell wall. It is an important component of the cell wall and the second most abundant macromolecular polymer, accounting for about 30% of the organic carbon content. Lignin plays an important role in plant growth and development. On the one hand, it can enhance the mechanical strength of plants, provide support for plant growth and development, and promote the transport of minerals and water in vascular bundles; on the other hand, lignin participates in the response of plants to biotic and abiotic stresses, which helps to improve the stress resistance of plants. Cellulose is the main component of plant cell walls, accounting for about 33% of the total weight of plants. Its economic value can be summarized as food, fiber, paper, and bioenergy, all of which are closely related to human life. Therefore, cellulose is the most economically valuable cell wall component. Its structure is very simple, but its synthesis mechanism is extremely complex. Current research suggests that cellulose is composed of unbranched β-1,4-glucan chains, each containing up to 15,000 glucose residues. The glucan chains are bound together by hydrogen bonds and van der Waals forces and arranged in parallel. Every 36 glucan chains form a microfibril, which is further arranged and deposited to form the advanced structure of cellulose. Hemicellulose is the second most abundant polysaccharide in nature and plays an irreplaceable role in the growth and development of plants. Plants with high hemicellulose content not only have strong resistance to lodging, but also can greatly improve the utilization rate of renewable energy.

[0003] The formation network of the secondary cell wall is extremely complex and is regulated by multiple parties. It has been reported that transcription factors Tier 1, 2, and 3, including MYB or NAC transcription factors, play a vital role in secondary cell wall biosynthesis (Zhong and Ye, 2009; Kumar et al. 2016; Ohtani and Demura, 2019). Ubiquitination is also involved in the formation of the secondary cell wall. The subunit DDB1a of the E3 ubiquitin ligase complex (Beris et al. 2016), cotton GhHUB2 (Feng et al. 2018), and rice OsFBK1 (Borah and Khurana, 2018), as components of the SCF E3 ligase complex, have all been reported to directly or indirectly regulate secondary cell wall synthesis. So far, research on the regulation of secondary cell wall development by GPAT is still blank. Summary of the invention

[0004] The purpose of the present invention is to provide the use of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in regulating the thickness of plant secondary cell walls to solve the problems existing in the above-mentioned prior art. The present invention first discovered that mitochondrial GPAT1 gene and mitochondrial GPAT2 gene have the function of regulating the thickness of plant secondary cell walls.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] The present invention provides application of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in regulating the thickness of plant secondary cell wall.

[0007] As an additional solution, the sequence number of the mitochondrial GPAT1 gene in TAIR (The Arabidopsis Information Resource) is AT1G06520; the sequence number of the mitochondrial GPAT2 gene in TAIR is AT1G02390.

[0008] The present invention provides a method for increasing the thickness of plant secondary cell walls, comprising the step of inhibiting the expression levels of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in the plant.

[0009] The invention provides the use of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in cultivating transgenic plants with thick secondary cell walls.

[0010] As an additional scheme, the present invention also provides a method for cultivating transgenic plants with thick secondary cell walls, comprising the steps of inhibiting the expression of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in the plant to obtain transgenic plants with thick secondary cell walls.

[0011] The present invention provides the application of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in regulating the content of plant lignin.

[0012] The invention provides a method for increasing the lignin content of a plant, comprising the step of inhibiting the expression of a mitochondrial GPAT1 gene and a mitochondrial GPAT2 gene in the plant.

[0013] The invention provides the use of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in cultivating transgenic plants with high lignin content.

[0014] As an additional scheme, the present invention also provides a method for cultivating a transgenic plant with a high lignin content, comprising the steps of inhibiting the expression of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in the plant to obtain a transgenic plant with a high lignin content.

[0015] The invention provides application of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in regulating plant cellulose content.

[0016] The invention provides a method for increasing the cellulose content of plants, comprising the step of inhibiting the expression of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in the plants.

[0017] The invention provides the use of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in cultivating transgenic plants with high cellulose content.

[0018] As an additional scheme, the present invention also provides a method for cultivating a transgenic plant with a high cellulose content, comprising the steps of inhibiting the expression of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in the plant to obtain the transgenic plant with a high lignin content.

[0019] Preferably, the plant is Arabidopsis thaliana.

[0020] As an additional solution, the present invention provides the use of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in regulating plant drought tolerance.

[0021] Further preferably, the plant is Arabidopsis thaliana.

[0022] As an additional scheme, the present invention provides a method for improving drought tolerance of plants, comprising the step of inhibiting the expression levels of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in the plant.

[0023] Further preferably, the plant is Arabidopsis thaliana.

[0024] As an additional solution, the present invention provides the use of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in cultivating drought-resistant transgenic plants.

[0025] Further preferably, the plant is Arabidopsis thaliana.

[0026] As an additional scheme, the present invention provides a method for cultivating drought-tolerant transgenic plants, comprising the steps of inhibiting the expression of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in the plant to obtain the drought-tolerant transgenic plants.

[0027] Further preferably, the plant is Arabidopsis thaliana.

[0028] As an additional solution, the present invention provides the use of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in cultivating drought-resistant transgenic plants.

[0029] Further preferably, the plant is Arabidopsis thaliana.

[0030] The present invention discloses the following technical effects:

[0031] The present invention has discovered for the first time that the mitochondrial GPAT1 gene and the mitochondrial GPAT2 gene have the function of regulating the thickness of the secondary cell wall of plants, which is specifically embodied in that the mitochondrial GPAT1 gene and the mitochondrial GPAT2 gene regulate the formation of the secondary cell wall by negatively regulating the genes related to lignin and cellulose biosynthesis. The results of the specific embodiments of the present invention show that when the mitochondrial GPAT1 gene and the mitochondrial GPAT2 gene are missing, the lignin and cellulose synthesis genes are upregulated, and a large amount of lignin and cellulose accumulate in the cell walls of the Arabidopsis double mutant gpat1 gpat2 seedlings, and the cell walls become thicker and harder, resulting in a harder texture of the cotyledons. It can be seen that the mitochondrial GPAT1 gene and the mitochondrial GPAT2 gene can be used to cultivate transgenic plants with thick secondary cell walls, providing a new path for the cultivation of new plant varieties. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1Mitochondrial GPAT1 and GPAT2 genes regulate the synthesis of lignin, where A is the cotyledons and hypocotyls of wild-type Arabidopsis seedlings (right) and Arabidopsis double mutant gpat1 gpat2 seedlings (left) stained with phloroglucinol, scale bar = 500 μm; B is the roots of wild-type Arabidopsis seedlings (right) and Arabidopsis double mutant gpat1 gpat2 seedlings (left) stained with phloroglucinol; C is the quantitative analysis result of lignin content, *** indicates p < 0.001; D is the real-time quantitative PCR (qPCR) result of lignin biosynthesis genes; all data are expressed as the mean ± standard deviation of three biological independent samples, and three independent experiments were performed with similar results; one-way ANOVA was used for statistical analysis; * indicates p < 0.05, ** indicates p < 0.01, *** indicates p < 0.001, ns indicates no significant difference; WT is wild-type Arabidopsis, gpat1 gpat2 is Arabidopsis double mutant gpat1 gpat2;

[0034] Figure 2 Comparison of lignin extracts and cellulose solutions from different seedlings; A is a comparison of lignin extracts; B is a comparison of cellulose extracts, and the lower right corner is the precipitation during the cellulose extraction process; Blank is a blank control, WT is wild-type Arabidopsis, and gpat1 gpat2 is the Arabidopsis double mutant gpat1 gpat2;

[0035] Figure 3 Mitochondrial GPAT1 and GPAT2 genes regulate cellulose synthesis; A is the cotyledons and hypocotyls of wild-type Arabidopsis seedlings (right) and Arabidopsis double mutant gpat1 gpat2 seedlings (left) stained by zinc chloride iodine method, scale bar = 500 μm; B is the result of cellulose content analysis by cellulose content determination kit, *** indicates p < 0.05; C is the qPCR result of lignin biosynthesis gene, all data are expressed as the mean ± standard deviation of three biological independent samples, three independent experiments were performed, the results were similar, and one-way ANOVA was used for statistical analysis, ** indicates p < 0.01, *** indicates p < 0.001, ns indicates no significant difference; WT is wild-type Arabidopsis, gpat1 gpat2 is Arabidopsis double mutant gpat1 gpat2;

[0036] Figure 4The staining images and thickness quantitative analysis of cotyledon cell walls of wild-type Arabidopsis and Arabidopsis double mutant gpat1 gpat2 seedlings; A is the transmission electron microscopy image of the adaxial surface of cotyledons of wild-type Arabidopsis and Arabidopsis double mutant gpat1 gpat2, CW is the cell wall, the black arrow indicates the cuticle, and the scale bar = 200nm; B is the quantitative analysis of cell wall thickness of wild-type Arabidopsis and Arabidopsis double mutant gpat1 gpat2; *** indicates P < 0.001; WT is wild-type Arabidopsis, and gpat1 gpat2 is the Arabidopsis double mutant gpat1 gpat2;

[0037] Figure 5 The results of an investigation on the sensitivity of wild-type Arabidopsis, the Arabidopsis double mutant gpat1 gpat2, the Arabidopsis complementation line GPAT1::gpat1gpat2 and the Arabidopsis complementation line GPAT2::gpat1 gpat2 to water loss. All data are expressed as the mean ± standard deviation of three biological independent samples. One-way ANOVA was used for statistical analysis. *** indicates p < 0.001. WT is wild-type Arabidopsis, gpat1 is the Arabidopsis mutant gpat1, gpat2 is the Arabidopsis mutant gpat2, gpat1 gpat2 is the Arabidopsis double mutant gpat1 gpat2, GPAT1::gpat1 gpat2 is the Arabidopsis complementation line GPAT1::gpat1 gpat2, and GPAT2::gpat1 gpat2 is the Arabidopsis complementation line GPAT2::gpat1 gpat2. DETAILED DESCRIPTION

[0038] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0039] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0040] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0041] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0042] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0043] Example 1

[0044] 1. Plant materials

[0045] The Arabidopsis double mutant gpat1 gpat2, the Arabidopsis complementation line GPAT1::gpat1 gpat2 and the Arabidopsis complementation line GPAT2::gpat1 gpat2 are disclosed in the document "Mitochondrial GPAT-derived LPA controls auxin-dependent embryonic and postembryonic development" and are promised to be released to the public for 20 years.

[0046] 2. Plant material growth conditions

[0047] The seeds of the above plant materials and wild-type Arabidopsis were germinated on half-strength Murashige and Skoog (MS) medium and, after two days of vernalization, transferred to a medium with a light intensity of 160 μmol·m -2 ·s -1 The seedlings were cultured in a light incubator with a day / night cycle of 14h / 10h (14h light, 10h dark) and a temperature of 23°C for 6 days. Afterwards, the seedlings were transferred to soil for further cultivation under the same conditions.

[0048] 3. Survey Methods

[0049] The lignin content was detected by the phloroglucinol method: 6-day-old Arabidopsis seedlings were immersed in lignin acidified solution for 10 min, and then an equal amount of phloroglucinol staining solution (McLean, China) was added dropwise to the acidified Arabidopsis seedlings. After standing, the staining of lignin in the Arabidopsis seedlings was observed under a stereomicroscope; then a lignin content determination kit (McLean, China) was used to investigate the lignin content in the Arabidopsis seedlings. The experimental steps were carried out according to the manufacturer's instructions of the kit, and the reagent without sample was used as the blank control (Blank).

[0050] The zinc chloride iodide method was used to detect the cellulose content: 6-day-old Arabidopsis seedlings were immersed in cellulose staining solution (Yuanye, China) for 5 min, and the cellulose staining in the Arabidopsis seedlings was observed under a stereomicroscope; then a cellulose content determination kit (McLean, China) was used to investigate the cellulose content in the Arabidopsis seedlings. The experimental steps were carried out according to the manufacturer's instructions of the kit, and the reagent without sample was used as the blank control (Blank).

[0051] The thickness of the cotyledon cell wall was observed by transmission electron microscopy (TEM) (HITACH HT7800, Japan). Specifically, the cotyledons of wild-type Arabidopsis and the Arabidopsis double mutant gpat1 gpat2 were fixed with 2.5% (w / v) glutaraldehyde in 0.2M PBS at 4°C for more than 2 hours. The samples were washed three times with 0.1M PBS and dehydrated through a series of gradient ethanol. Then, the cotyledons were embedded in epoxy resin and ultrathinly sectioned. Finally, the samples were placed on a copper grid, stained with uranyl acetate and lead citrate, and observed under a transmission electron microscope (80.0KV).

[0052] Before the water loss measurement, Arabidopsis seedlings were grown at 23°C for 1 week, and the water loss rate was calculated. The calculation formula of the water loss rate was: water loss rate = (initial weight - weight at a certain time point) / initial weight × 100%.

[0053] 4. RNA extraction and transcription analysis

[0054] Total RNA was extracted from the cotyledons of wild-type Arabidopsis thaliana and the Arabidopsis thaliana double mutant gpat1 gpat2 using the RNA-easy Isolation Reagent Kit (Novozyme, China). Ⅱ1st Strand cDNA Synthesis Kit (Yisheng, China) was used to synthesize the first strand cDNA. qPCR SYBR Green Master Mix (no rox) (Yisheng, China) was used for quantitative real-time fluorescence quantitative PCR (qPCR). ACTIN2 was used as an internal reference and the relative quantitative results were compared by the cycle threshold method (2 -ΔΔCt ) presents the average normalized transcription level. The detection was performed using the Gentier 96E / 96R system (Tianlong, China). The primer sequences used for qPCR and the accession numbers of the genes are shown in Table 1.

[0055] Table 1 Primers and gene accession numbers used in this example

[0056]

[0057]

[0058]

[0059] 5. Data Analysis

[0060] Statistical analysis was performed using IBM SPSS Statistics 25. Means were compared using one-way analysis of variance (ANOVA). Quantitative analysis of cell wall thickness was performed using ImageJ software.

[0061] 6. Results and Analysis

[0062] 6.1. Mitochondrial GPAT1 and GPAT2 genes regulate secondary cell wall (SCW) formation

[0063] In this example, phloroglucinol was used to dye wild-type Arabidopsis and Arabidopsis double mutant gpat1 gpat2 seedlings. Phloroglucinol is a lignin-specific dye. After dyeing, different degrees of lignification will appear red or purple-red. The stronger the degree of lignification, the darker the color. The results showed that the cotyledons and hypocotyls of Arabidopsis double mutant gpat1 gpat2 seedlings were darker than those of wild-type Arabidopsis, while there was no significant difference in the color of their roots ( Figure 1 In addition, the total lignin content was detected using a kit, and it was found that the total lignin content of the Arabidopsis double mutant gpat1 gpat2 seedlings was significantly higher than that of the wild-type Arabidopsis ( Figure 1 C and Figure 2 Therefore, we can conclude that mitochondrial GPAT1 and mitochondrial GPAT2 genes play a negative regulatory role on lignin content.

[0064] Afterwards, the cellulose content of wild-type Arabidopsis and Arabidopsis double mutant gpat1 gpat2 seedlings was analyzed by zinc chloride iodine method. The cotyledons and hypocotyls of Arabidopsis double mutant gpat1 gpat2 seedlings were significantly darker than those of wild-type Arabidopsis, indicating that the cellulose content of Arabidopsis double mutant gpat1 gpat2 seedlings was higher than that of wild-type Arabidopsis ( Figure 3 Further, to make this conclusion clearer, this example analyzed the cellulose content of wild-type Arabidopsis and Arabidopsis double mutant gpat1 gpat2 seedlings, and also found that the cellulose content of Arabidopsis double mutant gpat1 gpat2 seedlings was higher than that of wild-type Arabidopsis ( Figure 3 B and Figure 2 B).

[0065] To analyze how mitochondrial GPAT1 and mitochondrial GPAT2 genes regulate lignin and cellulose content, qPCR detection of lignin and cellulose synthesis genes in cotyledons of wild-type Arabidopsis and Arabidopsis double mutant gpat1 gpat2 seedlings was performed. For lignin synthesis, this example selected several genes from the PAL, C4H, 4CL, CCR, CAD, F5H, COM and LAC families to detect transcription levels. The results showed that, except for LAC15, almost all genes were upregulated, with LAC12 having the highest upregulation, followed by PAL3 ( Figure 1 D in the figure). For cellulose synthesis, nine genes of the CESA family were selected in this example, among which CESA4, CESA8, and CESA9 were significantly upregulated in the Arabidopsis double mutant gpat1 gpat2 seedlings, while CESA1 and CESA6 were slightly downregulated ( Figure 3 C).

[0066] In order to observe the epidermal structure more clearly, this example used transmission electron microscopy (TEM) to observe the cotyledons of 20-day-old wild-type Arabidopsis and Arabidopsis double mutant gpat1gpat2 seedlings. The results showed that the cell wall thickness of the cotyledons of the Arabidopsis double mutant gpat1 gpat2 seedlings was significantly higher than that of the wild-type Arabidopsis ( Figure 4 ).

[0067] These results indicate that mitochondrial GPAT1 and mitochondrial GPAT2 genes negatively regulate lignin and cellulose synthesis. When mitochondrial GPAT1 and mitochondrial GPAT2 genes are missing, several lignin and cellulose synthesis genes are upregulated, and a large amount of lignin and cellulose accumulate in the cell walls of Arabidopsis double mutant gpat1 gpat2 seedlings, and the cell walls become thicker and harder, resulting in a harder texture of the cotyledons, which confirms the reason for the thickening of the cell walls.

[0068] 6.2 Mitochondrial GPAT1 and GPAT2 genes maintain plant water balance

[0069] In order to explore whether the loss of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene affects the response of plants to water stress, the water loss of seedlings was measured in this example. The results showed that the water loss rate of Arabidopsis double mutant gpat1 gpat2 seedlings was slower than that of wild-type Arabidopsis, Arabidopsis complementation line GPAT1::gpat1 gpat2 and Arabidopsis complementation line GPAT2::gpat1gpat2 ( Figure 5 ), the Arabidopsis double mutant gpat1 gpat2 can adapt to more drought conditions. This shows that mitochondrial GPAT1 and mitochondrial GPAT2 genes can be used to cultivate drought-tolerant plants.

[0070] From the above, we can see that changes in cell arm thickness will lead to imbalance in plant water metabolism. The loss of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene promotes the synthesis of lignin and cellulose. The increase in lignin and cellulose content leads to thickening of cell walls, which can achieve the purpose of regulating plant drought tolerance.

[0071] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. Application of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in regulating the thickness of plant secondary cell walls.

2. A method for increasing the thickness of plant secondary cell walls, characterized in that: The method comprises the step of inhibiting the expression levels of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in the plant.

3. Application of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in cultivating transgenic plants with thick secondary cell walls.

4. Application of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in regulating plant lignin content.

5. A method for increasing the lignin content of plants, characterized in that: The method comprises the step of inhibiting the expression levels of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in the plant.

6. Application of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in cultivating transgenic plants with high lignin content.

7. Application of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in regulating plant cellulose content.

8. A method for increasing the cellulose content of plants, characterized in that: The method comprises the step of inhibiting the expression levels of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in the plant.

9. Application of mitochondrial GPAT1 gene and mitochondrial GPAT2 gene in cultivating transgenic plants with high cellulose content.

10. The application according to claim 1, the application according to claim 3, the application according to claim 4, the application according to claim 6, the application according to claim 7 or the application according to claim 9, characterized in that: The plant is Arabidopsis thaliana.

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