P-319 - Functional analysis of cross-kingdom small RNAs in the establishment of beneficial plant symbioses

The beneficial root endophyte Serendipita indica (Si) interacts with a broad range of plant hosts, including model plant and crop species. During the interaction with Arabidopsis thaliana (At) and Brachypodium distachyon (Bd), we have previously detected plant small (s)RNA molecules with regulatory roles on endogenous gene targets, as well as sRNAs of Si that have cross-kingdom function in host plants. Beyond bulk root expression, we specifically investigated the sRNAs co-isolated from major Argonaute (AGO) proteins present in plant roots. Taken together, our data showed that sRNAs seem to be interaction-specific between Si-colonized roots of At and Bd. Notably, target transcripts of these sRNAs are broadly conserved in At and Bd. They are commonly found in pathways regulating interaction with pathogenic and non-pathogenic microbes, hormonal signalling and abiotic stress response. In order to further functionally validate sRNA activities, we applied a protoplast-based assay and determined the participation of Si sRNAs in plant hormone cross-talk and plant stress adaptation. Considering the broad spectrum of plants that Si interacts with, our approach can help to decipher general mechanisms employed by Si to activate benefits in its host plants, including crops.