Barley stripe mosaic virus γb protein targets thioredoxin h-type 1 to dampen SA-mediated antiviral defenses

Salicylic acid (SA) acts as a signaling molecule to perceive and defend against pathogen infections. Accordingly, pathogens evolve versatile strategies to disrupt the SA-mediated signal transduction. However, it is necessary to further characterize how plant viruses manipulate the SA-dependent defense responses. Here, we show that Barley stripe mosaic virus (BSMV) infection activates SA-mediated defense signaling pathway and upregulates the expression of Nicotiana benthamiana thioredoxin h-type 1 (NbTRXh1). The γb protein interacts directly with NbTRXh1 in vivo and in vitro . Overexpression of NbTRXh1, but not a reductase-defective mutant, impedes BSMV infection, whereas low NbTRXh1 expression level results in increased viral accumulation. Similar with its orthologues in Arabidopsis , NbTRXh1 also plays an essential role in SA signaling transduction in N. benthamiana . To counteract NbTRXh1-mediated defenses, the BSMV γb protein targets NbTRXh1 to dampen its reductase activity and thereby impairing downstream SA defense genes expression to optimize viral cell-to-cell movement. We also found that NbTRXh1-mediated resistance defends against Lychnis ringspot virus , Beet black scorch virus , and Beet necrotic yellow vein virus . Taken together, our results reveal a novel role for the multifunctional γb protein in counteracting plant defense responses, and broadens the broad-spectrum antibiotic role of SA signaling pathway. One sentence summary BSMV γb protein impairs NbTRXh1 reductase activity and dampen downstream SA-related genes expression to facilitate viral cell-to-cell movement.