A virus-derived siRNA activates plant immunity by interfering with ROS scavenging.

Virus-derived small interference RNAs (vsiRNAs) can not only suppress virus infection in plant via induction of RNA silencing but also enhance virus infection via regulation of host defensive gene expressions. The underlying mechanism(s) controlling the vsiRNA-mediated host immunity or susceptibility remain largely unknown. In this study, we prepared several transgenic wheat lines using four artificial microRNA expression vectors carrying vsiRNAs from Wheat yellow mosaic virus (WYMV) RNA1. Laboratory and field tests showed that two transgenic wheat lines expressing amiRNA1 were highly resistant to WYMV infection. Further analyses showed that vsiRNA1 could modulate the expression of a wheat thioredoxin-like (TaAAED1) gene, a negative regulator of reactive oxygen species (ROS) production in chloroplast. The function of TaAAED1 in ROS scavenging could be suppressed by vsiRNA1 in a dose-dependent manner. In addition, transgenic expression of amiRNA1 in wheat results in a broad-spectrum disease resistance to Chinese wheat mosaic virus, Barley stripe mosaic virus, and Puccinia striiformis f. sp. tritici infection, suggesting that vsiRNA1 is involved in wheat immunity via ROS signal. Collectively, these findings reveal a previously unidentified mechanism underlying the arm-race between viruses and plants.