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Effect of ACC deaminase engineered endophytes on plant growth in drought and high salinity conditions

An illustration of our engineered endophytes fighting drought and salt stresses in the roots of a model plant!

Due to impending climate change related variation in rainfall, increased drought and soil salinities are predicted to become serious problems that lead to reduced crop yields from osmotic stress. In environments with high salinity and dry soil, plants respond by producing more ethylene, which engages regulatory pathways leading to premature senescence. Beneficial microbial endophytes are thought to increase the stress tolerance of plants in part by modulating signals from the ethylene pathway. For example, endophytes inside the roots of plants are known to secrete the enzyme ACC deaminase (ACCD), which converts 1-aminocyclopropane-1-carboxylate (ACC), the precursor to ethylene, into α-ketobutyrate and ammonia. The degradation of ACC reduces the formation of ethylene, thereby delaying the onset of senescence.

We seek to import efficient ACCD genes into endophytic bacteria that lack this pathway. Optimized ACCD genes from bacteria and fungi will be inserted into endophytic bacteria taken from grass roots. Brachypodium distachyon, a model grass species, will be inoculated with these bacteria to compare growth to a control plant. Another focus is to identify as many transformable endophytes as possible. This will be done by collecting root samples of common grasses, harvesting bacteria, sequencing for identification, and screening for ACCD activity. ACCD genes from numerous sources will be either amplified from culture or synthesized, then assembled and inserted into endophytic grassroots bacteria. Then these bacteria will be tested on B. distachyon to show increased growth. If such engineered endophytes confer additional stress tolerance onto B. distachyon, this technique may be a useful approach to boost crop yields, especially in developing countries and other areas where irrigation practices are difficult. Engineering of endophytes provides a way to promote plant growth without actually engineering plant genes themselves. This may improve public perception and thus development speed.