The RING-finger ubiquitin E3 ligase RFEL1 targets wheat NPR3 for degradation to confer broad-spectrum resistance against biotrophic fungal pathogens

Broad-spectrum resistance (BSR) is highly sought after for the effective management of crop diseases. However, genes suitable for developing BSR remain scarce. In this study, we demonstrate the development of BSR to wheat yellow rust (YR), powdery mildew (PM), and leaf rust (LR) diseases elicited by three biotrophic fungal pathogens using a newly defined module, namely, RFEL1-NPR3. RFEL1 is an active RING-finger E3 ubiquitin ligase identified in diploid and polyploid wheat species, which ubiquitinates and promotes the degradation of wheat NPR3 (TaNPR3), an important negative immune regulator conserved in higher plants, via the 26S proteasome system. Downregulation of TaNPR3 by either overexpressing RFEL1 or knocking out TaNPR3 confers strong resistance against four different YR races as well as the PM and LR diseases without adverse effects on wheat growth and yield traits. Notably, the enhanced disease resistance exhibited by RFEL1-overexpressing and TaNPR3-knockout lines is correlated with increased expression of defense related genes and elevated stability of NPR1, a pivotal positive regulator of plant immune signaling. Our findings underscore the importance of ubiquitination-dependent NPR3 degradation in plant immunity and advocate for the application of the RFEL1-NPR3 module in engineering BSR against biotrophic fungal pathogens in wheat and other crops.