VOLATILE COMPOUNDS RELEASED BY A BACTERIUM ACTIVATE A NONCANONICAL PATHWAY FOR AUXIN BIOSYNTHESIS AND CHANGE ROOT ARCHITECTURE AND GROWTH IN PLANTS

BURGOS HERRERA, GONZALO; PAGNUSSAT LA; DO NASCIMENTO MAURO; CURATTI, L.

Congreso; SAMIGE 2023; 2023

Some soil bacteria release diffusible and volatile organic compounds (VOCs) which exertsome growth promotion activity by poorly understood mechanisms. During the last years,our group isolated the actinobacterium Microbacterium sp, strain 15III (MB15III) whichpresented, in a dose-dependent way, a dramatic effect on wheat growth from stronginhibition to moderate growth promotion. Here, we report a similar effect on growth ofArabidopsis thaliana seedlings. Microbacterium also exerted these effects both by diffusionof compounds, apparently indole-3 acetic acid (AIA) and by VOCs. VOCs produced byMB15II could be identified by GC-MS as methanethiol, dimethyl sulfide and dimethylmethane dithiol, among others. Assays using transgenic lines deficient in AIA sensing (tir1-1afb2,3) or synthesis (yuc3,5,6,7,8), and reporter plants (DR5::GUS) for AIA sensingindicated that the response of plants to exposure either to diffusible or VOCs compounds ismediated by exogenous AIA sensing, and in the case of VOCs also involve endogenoussynthesis of the phytohormone by plants. A proteomic analysis, further confirmed by qRTPCR, showed that plants, in which growth was strongly inhibited by VPCs, presented aremarkable increase (about 100-fold) of the expression of NIT1 and NIT2 genes, whichencode for the enzymes responsible for a non-canonical pathway of AIA biosynthesis inplants. Expression of genes for thiols metabolism, mostly glutathione-S-transferases, and amoderate increase in the expression of several other genes, was also observed.To the best of our knowledge, bacterial stimulation of strong changes in root architectureand plant growth, mediated by VOCs that activate a non-canonical pathway for AIA has notbeen described before. These results will open new venues of research towardsunderstanding the mechanisms of bacterial-plant interactions at the molecular level.