A secreted glycoside hydrolase of Puccinia triticina modulates fungal pathogenesis and host immunity

1. A glycoside hydrolase PtGH26_1 corresponds with the pathogenesis of Puccinia triticina . 2. PtGH26_1 shows cellulase activity and is an effector protein that inhibits plant immune responses. 3. PtGH26_1 interacts with the Fantastic Four-like protein (TaFAF) in wheat, which positively regulates host resistance to Pt . Many species of the obligate biotrophic rust fungi often cause destructive diseases on crops. Glycoside hydrolases (GHs) in phytopathogens have been widely recognized for their crucial roles in breaking through the plant's defense system. Despite this, the specific functions of most GHs in rust fungi remain largely uncharted. In this study, we examined a GH26 gene from the wheat leaf rust pathogen Puccinia triticina ( Pt ), designated PtGH26_1 , which exhibited highly induced expression during critical stages of host infection. PtGH26_1 demonstrated cellulase activity and contained a functional signal peptide, localized to both the plant cytoplasm and nucleus. When transiently expressed, PtGH26_1 inhibited Bcl2-associated X protein (Bax)-induced cell death, callose deposition, and the expression of defense-related genes in Nicotiana benthamiana . Additionally, infiltrating PtGH26_1 protein into wheat leaves compromised resistance to Pt and lessened hypersensitive responses. Silencing PtGH26_1 through host-induced gene silencing impaired fungal growth and virulence of Pt , leading to increased production of reactive oxygen species and activation of defense-related genes in wheat. Moreover, PtGH26_1 was shown to target one member of the Fantastic Four-like proteins in wheat (TaFAF), which positively regulated host resistance to Pt . Consequently, our findings indicate that PtGH26_1 is a significant virulence factor, potentially involved in breaching the barrier of plant cell walls and modulating host immune responses during Pt infection.