Mutations in PpAGO3 Lead to Enhanced Virulence of Phytophthora parasitica by Activation of 25-26 nt sRNA-Associated Effector Genes

Oomycetes represent a unique group of plant pathogens that are destructive to a wide range of crops and natural ecosystems. species possess active small RNA (sRNA) silencing pathways, but little is known about the biological roles of sRNAs and associated factors in pathogenicity. Here we show that an gene, , plays a major role in the regulation of effector genes hence the pathogenicity of . was unique among five predicted genes in , showing strong mycelium stage-specific expression. Using the CRISPR-Cas9 technology, we generated mutants that carried a deletion of 1, 2, or 3 copies of the N-terminal RGG motif (QRGGYD) but failed to obtain complete knockout mutants, which suggests its vital role in . These mutants showed increased pathogenicity on both and plants. Transcriptome and sRNA sequencing of and showed that these mutants were differentially accumulated with 25-26 nt sRNAs associated with 70 predicted cytoplasmic effector genes compared to the wild-type, of which 13 exhibited inverse correlation between gene expression and 25-26 nt sRNA accumulation. Transient overexpression of the upregulated RXLR effector genes, and identified in the mutants and , strongly enhanced susceptibility to . Our results suggest that PpAGO3 functions together with 25-26 nt sRNAs to confer dynamic expression regulation of effector genes in , thereby contributing to infection and pathogenicity of the pathogen.