Fungi adapted to metabolize phosphite as a source of phosphorus

Abstract

System, including methods and compositions, for making and using fungi that are adapted transgenically to metabolize phosphite as a source of phosphorus for supporting growth.

Description

CROSS-REFERENCES TO PRIORITY APPLICATIONS[0001]This application is a continuation of U.S. patent application Ser. No. 13 / 130,285, filed May 19, 2011, which in turn claims priority under 35 U.S.C. §371 to PCT Application Serial No. PCT / IB2009 / 007741, filed Nov. 19, 2009, which in turn claims priority to U.S. Provisional Patent Application Ser. No. 61 / 199,784, filed Nov. 19, 2008.[0002]Each of these priority documents is incorporated herein by reference in its entirety for all purposes.INTRODUCTION[0003]Phosphorus is an essential element for plant and fungal growth. This element, in oxidized form, is incorporated into many of the biomolecules in a plant or fungal cell, such as to provide genetic material, membranes, and molecular messengers, among others.[0004]Inorganic phosphate (Pi) is the primary source of phosphorus for plants. Accordingly, phosphate-based fertilizers offer a cheap and widely used approach to enhancing plant growth. However, phosphate-based fertilizers come from a...

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Benefits of technology

[0004]Inorganic phosphate (Pi) is the primary source of phosphorus for plants. Accordingly, phosphate-based fertilizers offer a cheap and widely used approach to enhancing plant growth. However, phosphate-based fertilizers come from a non-renewable resource that has been projected to be depleted in the next seventy to one hundred years, or sooner if the usage rate increases faster than expected.

[0007]Phosphite can promote plant growth indirectly. For example, phosphite is used as an anti-fungal agent (a fungicide) on cultivated plants. Phosphite is thought to prevent diseases caused by oomycetes (water molds) on such diverse plants as potato, tobacco, avocado, and papaya, among others. Phosphite thus may promote plant growth, not directly as a plant nutrient, but by protecting plants from fungal pathogens that would otherwise affect plant growth. Nevertheless, phosphite-based fungicides often are labeled as fertilizers. This mislabeling may be encouraged by government regulations that make the approval process shorter and less complex if manufacturers characterize fungicides as fertilizers.

Problems solved by technology

However, phosphate-based fertilizers come from a non-renewable resource that has been projected to be depleted in the next seventy to one hundred years, or sooner if the usage rate increases faster than expected.

The phosphate-based fertilizers common to modern agriculture generally cannot be used efficiently by cultivated plants, due to several important factors.

First, phosphate is highly reactive and can form insoluble complexes with many soil components, which reduces the amount of available phosphorus.

Second, soil microorganisms can rapidly convert phosphate into organic molecules that generally cannot be metabolized efficiently by plants, which reduces the amount of available phosphorus further.

Losses due to the conversion of phosphate into inorganic and organic forms that are not readily available for plant uptake and utilization, and competition from weeds, implies the use of excessive amounts of phosphate fertilizer, which not only increases production costs but also causes severe ecological problems.

However, there apparently are no reports of any enzymes in plants that can metabolize phosphite into phosphate, the primary source of phosphorus in plants.

Moreover, even during phosphate starvation, phosphite apparently cannot satisfy the phosphorus nutritional requirements of the plant.

Accordingly, in spite of similarities to phosphate, phosphite is a form of phosphorus that generally cannot be metabolized directly by plants, and thus is not a plant nutrient.

Nevertheless, phosphite “fertilizers” are sold commercially, even though there appears be no proof or even an indication in the scientific literature that plants can assimilate phosphite.

The concentration of phosphite in contact with plants may be a critical factor for phosphite effectiveness because too much phosphite can be toxic to plants.

Phosphite toxicity thus may be due to (1) reduced assimilation of phosphate by plants, in combination with (2) an inability to use phosphite as a source of phosphorus by oxidation to phosphate, which causes phosphite accumulation in the plants.

However, each selection system has disadvantages.

For example, each selection system can have problems with toxicity.

Also, selection with antibiotics may be inefficient since plants can have alternate resistance mechanisms.

Furthermore, except for the selection system using phosphinothricin, none of the selection systems provides a “universal” selectable marker for most or all plants.

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