Diacetyl determines plant-bacteria relation via phosphate-dependent modulation of plant immunity

Plants establish mutualistic association with beneficial microbes while deploy the immune system to defend against pathogens. Little is known about the interplay between mutualism and immunity and about the mediator molecules. Here we show that plants respond differently to a bacterial volatile compound through integral modulation of the immune system and the phosphate starvation response (PSR) system, resulting in either mutualism or immunity. We found that the same exposure of a recognized plant growth-promoting rhizobacterium unexpectedly causes either beneficial or deleterious effects to plants. The beneficial-to-deleterious transition is dependent on plant nutrition of phosphorus (P) and is mediated by diacetyl (DA), a bacterial volatile compound. In P-sufficient plants, DA partially suppresses plant production of reactive oxygen species (ROS) and enhances symbiont colonization without compromising disease resistance. In P-deficient plants, DA elevates phytohormone-mediated immunity and consequently causes plant hypersensitivity to P deficiency. Therefore, DA affects the types of relation between plants and certain rhizobacteria in a way that depends on plant PSR system and phytohormone-mediated immunity. RNA-Seq of 6 samples, each has 2 replicates. The first four samples are for GMVs treatment, HMZ008_0.05 denotes, plants grown on nutrient deficient medium (1/20th strength MS medium) and samples HMZ008_0.5, refer to plant grown on 1/2 MS medium. C= mock samples and T= samples treated with GMVs. Last two samples are plants grown on 1/2 strength MS medium analysed for effect of diacetyl on platnt transcriptome, HMZ014_CK=mock and HMZ014_Dione= plants treated with 200µM Diacetyl.