Insights into Plant Growth Modulation by Microbacterium Through Volatile Organic Compounds and Plant Auxin Biosynthesis and Signaling

Abstract

Food security and environmental sustainability require innovative agricultural approaches, with plant growth-promotingmicrobes offering promising solutions. This study explores the growth modulation of plants by Microbacterium sp. MB15through secreted compounds, distinguishing between the effects of total diffusible substances and volatile organic compounds (VOCs). Microbacterium sp. MB15 exhibited a dose-dependent influence on wheat and Arabidopsis germination,growth, and root architecture, shifting from stimulation at low exposure levels to inhibition at higher concentrations. Totaldiffusible compounds, including auxin produced by the bacterium, exert their effect on Arabidopsis through the TIR1/AFB pathway and partially require the YUCCA genes. Microbacterium sp. MB15 VOCs, comprising ethanol, aceticacid, ethyl acetate, methanethiol and dimethyldisulfide, also elicited strong modulation of seed germination and seedlinggrowth through mechanisms only partially dependent on TIR1/AFB and YUCCA. A proteomic analysis of seedlingsexposed to bacterial VOCs (ProteomeXchange # PXD069087) indicated stimulation of carbohydrate and lipid mobilization, overexpression of proteins associated with a non-canonical auxin pathway, metabolism of indolic glucosinolates,defense responses, and sulfur-redox homeostasis. Additionally, high exposure to VOCs led to repression of genes forphotosynthesis and chloroplast integrity. These findings help unravel the complex molecular responses underlying plantmicrobe interactions.