<i>Streptomyces</i> Volatiles Alter Auxin/Cytokinin Signaling, Root Architecture, and Growth Rate in <i>Arabidopsis thaliana</i> via Signaling Through the <i>KISS ME DEADLY</i> Gene Family

Microbial volatile metabolites can enhance plant growth, yet the mechanisms by which plants perceive and transduce these signals are unknown. Growth of <i>Arabidopsis thaliana</i> Col-0 seedlings was found to be stimulated by volatiles from the soil bacterium <i>Streptomyces coelicolor</i>. To investigate volatile-responding candidate signaling molecules and genes, cultivation of seedlings in gas-phase contact with <i>S. coelicolor</i> genotypes was combined with GC-MS and plant transcriptomics. Components potentially involved were further studied using pure compounds and <i>A. thaliana</i> T-DNA mutants. Application of volatiles from <i>S. coelicolor</i> enhanced the growth of <i>A. thaliana</i> seedlings primarily by stimulating lateral root growth rate and inhibiting primary root extension. Concurrently, a family-wide induction of the Kelch-repeat F-box gene family <i>KISS ME DEADLY</i> (<i>KMD</i>) was observed. <i>A. thaliana</i> genotypes with a loss of function for the <i>KMD</i> family or other alterations of auxin/cytokinin signaling homeostasis suppressed the root response to both <i>S. coelicolor</i> total volatiles and the common microbial volatile 3-octanone. The results reveal a novel function of <i>KMD</i>s in mediating plant growth stimulation in response to volatile stimulation that alters auxin/cytokinin signaling and emphasize rhizospheric microbials as potential indicators of soil status to plants.