Phytophthora infestans Argonaute 1 binds micro RNA and small RNA s from effector genes and transposable elements

Phytophthora spp. encode large sets of effector proteins and distinct populations of small RNA s ( sRNA s). Recent evidence has suggested that pathogen‐derived sRNA s can modulate the expression of plant defense genes. Here, we studied the sRNA classes and functions associated with Phytophthora infestans Argonaute (Ago) proteins. sRNA s were co‐immunoprecipitated with three PiAgo proteins and deep sequenced. Twenty‐ to twenty‐two‐nucleotide (nt) sRNA s were identified as the main interaction partners of PiAgo1 and high enrichment of 24–26‐nt sRNA s was seen in the PiAgo4‐bound sample. The frequencies and sizes of transposable element ( TE )‐derived sRNA s in the different PiAgo libraries suggested diversified roles of the PiAgo proteins in the control of different TE classes. We further provide evidence for the involvement of PiAgo1 in the P. infestans micro RNA (mi RNA ) pathway. Protein‐coding genes are probably regulated by the shared action of PiAgo1 and PiAgo5, as demonstrated by analysis of differential expression. An abundance of sRNA s from genes encoding host cell death‐inducing Crinkler ( CRN ) effectors was bound to PiAgo1, implicating this protein in the regulation of the expanded CRN gene family. The data suggest that PiAgo1 plays an essential role in gene regulation and that at least two RNA silencing pathways regulate TE s in the plant‐pathogenic oomycete P. infestans .