The additional unique ability of TuMV HC-Pro in inhibiting HEN1 activity for enhancing the autophagic AGO1 degradation in RNA silencing suppression

Genomes of potyviruses, the largest group of plant viruses, encode HC-Pro proteins that mediate RNA silencing suppression. HC-Pros may exhibit only 40% similarity between species, and induce different levels in autophagic ARGONAUTE1 (AGO1) degradation. Our data indicated that HC-Pro of turnip mosaic virus (HC-ProTu) could efficiently trigger AGO1 degradation through autophagy compared with HC-Pros of zucchini yellow mosaic virus (HC-ProZy) and tobacco etch virus (HC-ProTe). Furthermore, HC-ProTu, but not in HC-ProZy, forms a suppression body (S-body) to recruit AGO1 and HEN1, preventing those components from translocating into the nucleus. HC-ProTu, but not HC-ProZy and HC-ProTe, specifically inhibits HEN1 activity, resulting in unmethylated microRNAs (miRNAs) accumulating in the cytoplasm without loading into AGO1. Therefore, we hypothesize that HC-ProTu could enhance the autophagic AGO1 degradation due to the unique HEN1 inhibition interfering with RNA-inducing silencing complex (RISC) assembly.