[en] The metabolic roles of volatile organic compounds (VOCs) emitted by plant growth-promoting rhizobacteria (PGPR) and the identity of the molecules responsible for the growth promotion are still poorly documented. As well, the implication of microRNAs in root development is a recent discovery that deserves to be explored. In this study, the implication of microRNAs in the response of Brachypodium distachyon (L.) Beauv. Bd21 root architecture to rhizobacterial VOCs was investigated. Nineteen PGPR strains were screened to select those showing the strongest phenotypic effects. The strain Bacillus subtilis AP305-GB03 induced the most important promotion of biomass production and root development. Total RNA extraction and RT-qPCR analysis of microRNAs were performed on Bd21 root samples. The expression of miR160 a-d, miR164 f, miR167 c-d, miR397 b and miR399 a-b was measured in roots every 2 days during the first 10 days of Bd21 development, in the presence or absence of the bacterial VOCs. Differences in the expression profile of miR164 f and miR167 c-d were observed in the roots exposed to GB03 VOCs, as compared to the control. These differences could be correlated to the root system architecture modifications observed after 10 days of growth with GB03. miR397 b and miR399 a-b also showed differences in the expression profile of roots exposed to the bacterial VOCs. These microRNAs have been respectively involved in cold stress tolerance and in the response to phosphate starvation.
