The oligosaccharyltransferase TaOST1B promotes viral infection by enhancement of RNA silencing suppression in wheat.

Viral suppressors of RNA silencing (VSRs) are crucial for viral infection. Here, we show that a wheat (Triticum aestivum) oligosaccharyltransferase (TaOST1B) is associated with resistance to Wheat yellow mosaic virus (WYMV). TaOST1B interacts with WYMV-encoded P1 and enhances the VSR function of P1 by N-glycosylating its asparagine residue at position 116. This increases intranuclear accumulation of P1 through interaction with the nuclear transport protein TaIMP-α2 and blocks the interaction between calmodulin (CaM3) and CaM-binding transcriptional activator (CaMTA3) to suppress RNA interference. Nevertheless, nonglycosylated P1 loses its VSR function and forms aggregates triggering endoplasmic reticulum (ER) stress and is subsequently degraded by the 26S proteasome. A natural variant of TaOST1B fails to bind P1 and regulate its N-glycosylation, which induces ER stress and proteasome-mediated degradation to attenuate WYMV infection. Our study identifies an oligosaccharyltransferases as being utilized by VSR to promote viral infection, offering insights into the arms race between plants and viruses.