MicroRNAs as master regulators of the plant NB-LRR defense gene family via the production of phased, trans-acting siRNAs

Trans-acting siRNAs (tasiRNAs) are a class of plant small RNAs, and only a small number of tasiRNA loci have been identified in Arabidopsis. In this Resource/Methodology paper, Meyers and colleagues find that the legume Medicago, which requires a mechanism to suppress its immune response to nitrogen-fixing bacteria, encodes and produces a much larger number of tasiRNAs. These tasiRNAs regulate members of the NB-LRR class of disease resistance genes by targeting sequences encoding a highly conserved protein motif. Three microRNA (miRNA) families that target members of the same family of NB-LRR mRNAs at different conserved motifs were characterized. Thus, this study delineates novel aspects of miRNA regulation of gene silencing