TaR3H interacts with Pm21 and confers powdery mildew resistance.

Wheat powdery mildew [caused by Blumeria graminis f. sp. tritici (Bgt)] severely threatens global wheat production. Previously, we cloned the broad-spectrum wheat powdery mildew resistance gene Pm21 which encoded a typical nucleotide-binding leucine-rich repeat (NLR) immune receptor. In this study, we identified TaR3H as an interacting protein of the Pm21 coiled-coil (CC) domain (Pm21CC) and performed comprehensive biochemical and functional analysis to illustrate the defense pathway mediated by Pm21. TaR3H, a putative transcription factor, localizes to both the nucleus and plasma membrane, with its transcriptional activation function residing in the N-terminal region. We found that TaR3H interacts with Pm21CC, but not with full-length Pm21 (Pm21FL) in uninfected cells, whereas it interacts with both Pm21CC and Pm21FL during Bgt infection, suggesting that the protein folding state or activity of Pm21CC modulates its interaction. Functional studies demonstrated that silencing TaR3H in Pm21-carrying resistant materials compromised resistance to Bgt, while overexpression of TaR3H in the susceptible cultivar enhanced powdery mildew resistance. Integrated transcriptomic and DAP-seq analysis indicated that TaR3H-mediated resistance enhancement is associated with the hormone signaling pathway. This study reveals novel functions of TaR3H in the broad-spectrum powdery mildew resistance pathway, providing new insights into the molecular mechanism underlying Pm21-mediatd immunity.