Puccinia triticina effector Pt_20₆₃₆ triggers PCD in TcLr16 wheat promoted by TaLhcb4.1 via the ROS pathway

As an obligate biotrophic pathogen, Puccinia triticina (Pt) subverts wheat immunity via effector delivery. However, the molecular mechanisms underlying Pt effector-mediated wheat susceptibility remain largely unexplored. In this study, an effector Pt_20 that is induced expression at the early stage of Pt infection to wheat was identified. Interestingly, the Pt_20 gene exhibits two distinct transcriptional isoforms (Pt_20₆₃₆, Pt_20₈₀₇) among Pt races and both are localized in the nucleus, cytoplasm, and plasma membrane. Pt_20₆₃₆ was able to suppress BAX-mediated cell death in Nicotiana benthamiana, but Pt_20₈₀₇ was not. Importantly, Pt_20₆₃₆ triggers Lr16-dependent cell death, though Pt_20₈₀₇ does not trigger any immune response. We found that TaLhcb4.1 interacts with Pt_20₆₃₆, and Pt_20₆₃₆ inhibited the function of TaLhcb4.1 involved in wheat resistance to Pt via the ROS pathway. Furthermore, TaLhcb4.1 facilitates Pt_20₆₃₆-triggered immune responses in TcLr16 by promoting H₂O₂ accumulation. Overall, these findings demonstrate the dual role of Pt_20₆₃₆, it subverts TaLhcb4.1-mediated resistance while eliciting Lr16-recognized immune signaling, highlighting the complex interplay between fungal virulence and host defense during wheat-Pt interactions.