RNA silencing pathway components determine basal defense against Verticillium

CS-4.6 - The plant immune system is a well-known target of RNA silencing, particularly against viruses and bacteria. Data from our laboratory indicate that a functional RNA silencing pathway in the host plant is important for basal defense against the fungus Verticillium dahliae (Ellendorff et al., 2009). If, and how, V. dahliae targets RNA silencing to suppress host immunity remains unknown. The suppressor of gene silencing 2-1 mutant, sgs2-1, which is impaired in gene silencing, shows suppressed basal defense to V. dahliae when compared with wild-type plants. SGS2 encodes the RNA-dependent RNA polymerase (RdRP) RDR6 (Mourrain et al., 2000). RDR6 is involved in the biogenesis of trans-acting siRNAs. This process is initiated by miRNA-directed and Argonaute (AGO) protein-mediated cleavage of TAS gene transcripts. The small RNAs and their regulated transcript targe ts that are at the basis of the altered Verticillium susceptibility in the rdr6 mutants are unknown. By combining transcriptomics and small-RNA profiling we have identified differentially regulated gene transcripts and small-RNAs during V. dahliae infection of wild-type and sgs2-1 plants. We will present small RNAs and their reciprocal target transcripts that are differentially regulated in the rdr6 mutant upon inoculation with Verticillium dahliae when compared with inoculated wild-type plants. We postulate that some of the differentially regulated small RNAs and their corresponding target transcripts between wild-type and rdr6 mutant plants are key to the basal defense against V. dahliae. Ellendorff et al., 2009, J. Exp. Bot. 60 (2): 591-602. Mourrain et al., 2000, Cell 101: 533-542.