Argonaute 15 regulates immunity of potato to filamentous pathogens through transposon-derived small RNAs

Argonaute 15 (StAGO15) plays a crucial role in protecting potato plants from filamentous pathogens by regulating immunity through small RNA molecules derived from transposons. This gene, unique to Solanum species, is induced upon infection by these pathogens. However, the protective effect of StAGO15 can be suppressed when a specific 21-nt sequence within its PAZ-encoding region is targeted by artificial microRNA.

By examining the small RNAs associated with StAGO15 in response to infection by the pathogen Phytophthora infestans, researchers identified distinct differences between samples from plants exposed to the pathogen and those subjected to water inoculation. Notably, two categories of nonautonomous transposable elements (TEs) were found to be prominent in the pathogen-inoculated samples - miniature inverted-repeat transposable elements (MITEs) and short interspersed nuclear elements.

These TEs were associated with small RNAs that target complementary endogenous potato RNAs, including siRNA122.

SiRNA122 functions by binding to a cleavage site within the resistance gene StRES1, which encodes a protein involved in the plant's defense mechanisms. Interestingly, the production of siRNA122 is dependent on the presence of a specific 21-nt sequence within a MITE transposon. When this sequence is deleted, resistance to the pathogens is restored, highlighting the importance of this transposon-derived small RNA in the plant's immune response.

This discovery sheds new light on the intricate network of plant immune surveillance and demonstrates the potential for manipulating transposons to enhance disease resistance in crops.