Foliar application of a Streptomyces sp. on tomato plants: an insight into the induction of defence-related genes through RNA-Seq analysis

Microbial biocontrol agents (mBCAs) protect plants against a broad spectrum of pathogens through various mechanisms of action, including the activation of innate defence systems. The investigation of molecular mechanisms of plant resis¬tance triggered by mBCAs is crucial for implementing sus¬tainable disease management. Streptomycetes have drawn considerable attention for their potential as mBCAs; how¬ever, their use in foliar treatments to elicit plant resistance is still poorly investigated. RNA-Seq analysis was conducted to assess differential gene expression in tomato plants within 24 hours after applying Streptomyces sp. DLS2013. Our results showed a time-course up-regulation of genes related to defence pathways that are either SA or JA-dependent, and promoting the synthesis of antimicrobial metabolites (e.g., polyamines and phenolics). These findings suggest that DLS2013 preconditions tomato plants, therefore arm¬ing them against future challenging pests. To confirm this, foliar application of DLS2013, followed by the inoculation with the hemibiotrophic pathogen Pseudomonas syringae pv. tomato (Pst), significantly reduced bacterial speck sever¬ity by 67%, while no antagonistic effect of DLS2013 against Pst was observed in vitro. Lastly, the transcription profiling of six genes tied to different defence mechanisms showed an enhanced expression of genes involved in SA-depen-dent defence signalling (e.g., PR-1), alongside a decrease in JA-dependent defence responses in pre-treated plants challenged or not with Pst, possibly mediated by JAZ-25 repressor protein. Further studies are ongoing to investigate disease resistance induced by Streptomyces sp. DLS2013 against other pathogens and the potential regulatory mode of JAZ genes. This study has been financed by the Department of Life Sciences (University of Modena and Reggio Emilia; Italy), in the framework of the” Finanziamento FAR_DIP2022”.