Secreted Xylanase PstXyn1 Contributes to Stripe Rust Infection Possibly by Overcoming Cell Wall Barrier and Suppressing Defense Responses in Wheat

Puccinia striiformis f. sp. tritici (Pst) secretes a plethora of cell wall-degrading enzymes (CWDEs) to facilitate fungal invasion during infection. However, the functions and molecular mechanisms of the CWDEs from Pst remain unclear. In this study, we identified a secreted xylanase, named PstXyn1, with the GH10 domain. PstXyn1 was significantly up-regulated at the early infection stage of Pst. The signal peptide of PstXyn1 was confirmed to be functional. The purified PstXyn1 showed detectable xylanase activity. In addition, we found that PstXyn1-silenced wheat plants exhibited broad-spectrum resistance against multiple Pst pathotypes. Colloidal gold labeling and transcriptome sequencing analyses revealed that PstXyn1 contributed to xylan degradation in host cell walls and suppressed the expression of defense-related genes. Conclusively, our results indicate that PstXyn1 is secreted as an important virulence factor to overcome host cell wall barriers and compromise immune responses for fungal invasion, providing potential targets for improving wheat resistance to stripe rust.