Camalexin in the control of plant microbe interactions in the rhizosphere

Plants in their natural ecosystems interact with numerous microorganisms. They exude secondary metabolites from the roots to shape the composition and function of their microbiome. To identify plant genes responsible for modulation of microbiome function we used sulfatase activity in soil, which can be used as a measure of rhizosphere microbial activity. We observed that the activity in soil is differently affected by Arabidopsis accessions. Following a genome wide association analysis of the variation in sulfatase activity we identified a new gene involved in the biosynthesis network of camalexin, a sulfur-containing indolic defense compound. We showed that camalexin affects not only the microbiome activity in soil, but is also important for plant growth promoting effects of numerous bacterial strains. We further revealed that the new gene identified by GWAS, CYP71A27, does not have an enzymatic activity but its loss affects transcriptome and proteome of plants inoculated with a plant growth promoting bacteria. Thus, plants seem to use defense compounds not only against pathogens but also to modulate the function of their associated microbiome.