Promotion of Arabidopsis growth and flowering by Alternaria alternata volatile emissions is a photocontrolled process involving dramatic changes in the plant hormone

Abstract

Plants perceive biotic stimuli by recognizing different signaling substances originating from the interacting microorganisms. Some of them are volatile compounds. Volatile emissions from some rhizobacterial isolates promote growth in Arabidopsis by facilitating nutrient uptake, photosynthesis and defense responses, and by decreasing glucose sensing and ABA levels. Analyses of Arabidopsis mutants affected in hormone signaling have indicated possible involvement in the reaction to rhizobacterial volatiles. We found that the production of volatilespromoting plant growth is not restricted to some rhizobacteria, and that volatiles emitted by different microbial species ranging from Gram-negative and Gram-positive bacteria to different fungi (including plant pathogens and microbes normally not interacting with plants) promote both growth and accumulation of exceptionally high levels of starch in leaves of both mono- and di-cotyledonous plants. This phenomenon, initially designated as MIVOISAP (for MIcrobial VOlatiles Induced Starc Accumulation Process), involves changes in the leaf transcriptome and metabolome. To better understand MIVOISAP, we analyzed the effect of volatiles emitted by Alternaria alternata on Arabidopsis development. We found that itsvolatiles induce rapid growth, development of secondary roots and initiation of the flowering. Using different mutants we also observed that MIVOISAP down-regulated genes involved in light signaling and in the main hormone synthesis and signaling. We also carried out high throughput analyses of hormone content in root and leaves of plants exposed to A. altertata volatile emissions. The overall data showed that MIVOISAP is a photocontrolled process involving dramatic changes in the hormonome of the both plant organs.