The Arabidopsis thaliana sRNAs-mediated gene silencing machinery and its role on the establishment of a beneficial relationship with Trichoderma atroviride

Plants interact with a plethora of microbes to establish a pathogenic or beneficial relationship. To establish a relationship with plants, pathogens and beneficial microbes use effector molecules to suppress plant immunity. To defend from pathogens, plants have developed the induced systemic resistance, which is effective against necrotrophic pathogens, whereas the systemic acquired resistance is effective against hemibiotrophic and biotrophic microbes. In plants, the components of small RNAs (sRNAs) silencing-machinery, including Dicer-like (DCL), Argonaute (AGO), RNA-dependent RNA polymerase (RDR) and DNA-dependent RNA polymerase (POL) are involved in plant-microbe interaction. We evaluated a set of Arabidopsis thaliana sRNAs silencing-machinery mutants, to test whether they are involved in the beneficial interaction with Trichoderma atroviride. The Arabidopsis mutant ago2-1, ago6-2 pretreated with Trichoderma showed a wild-type (wt) growing phenotype compared to Col-0 treated plants, whereas the treatment of ago8-1, rdr2-1 and pol V seedlings with T. atroviride, affected the fungal plant growth promotion effect. Protection assays against phytopathogens Botrytis cinerea and Pseudomonas syringae Pst DC3000 respectively, showed that ago2-1 untreated seedlings with T. atroviride were more resistant to B. cinerea, and presented susceptibility to Pst DC3000. The pol V lines showed a susceptible phenotype to B. cinerea, but resistant to Pst DC3000. pol V plants treated with T. atroviride and challenged with B. cinerea presented a wt phenotype, but showed more susceptibility to Pst DC3000. The pretreatment of ago2-1 plants with Trichoderma turned them more susceptible to B. cinerea and did not respond to the bacterium. Furthermore, rdr2-1 mutants showed a wt phenotype to B. cinerea and Pst DC3000, however, the root treatment of these plants with T. atroviride presented a similar phenotype as compared to the wt with both pathogens, whereas ago7 showed the same phenotype to B. cinerea than the wt plants, and the pretreatment with Trichoderma showed less damage compared to Col-0.