Plant innate immunity depends on recognition of pathogen effectors and triggering of host defenses. Major classes of innate immune receptors, the nucleotide binding-leucine rich repeat receptors (NLRs) and leucine rich repeat (LRR) receptors are encoded by large families of resistance (R)-genes. NLR and LRRs are activated by recognition of specific pathogen effectors and once activated they trigger the hypersensitive cell-death response. While multiple NLRs and LRRs protect plants from diverse pathogens their inherent cell death activity and the large number of encoding R-genes in plant genomes require strict regulation.
Plant microRNAs (miRNAs) and small interfering RNAs (siRNAs) guide sequence-specific silencing of genes, repetitive DNA and viruses through Watson-Crick base pairing and play essential regulatory roles in development, genome function and host defense.
We discovered novel miRNA families whose members silence R-gene encoding NLRs and LRRs including those that confer resistance to the major pathogens of Solanaceae crops. Many of these novel miRNAs belong to a structurally and functionally unique class of 22-nt miRNAs and amplify silencing by triggering the production of secondary trans-acting siRNAs (tasiRNAs) from cleaved transcripts. The lab further showed that miRNA overexpression leads to attenuated R-gene mediated pathogen resistance. We propose that the R-gene miRNAs and tasiRNAs form a regulatory silencing network to fine tune pathogen defense responses and facilitate expansion and evolution of new NLRs.