The C4 protein encoded by Tomato leaf curl Yunnan virus interferes with mitogen-activated protein kinase cascade-related defense responses through inhibiting the dissociation of the ERECTA/BKI1 complex.

Mitogen-activated protein kinase (MAPK) cascades are involved in host defense against pathogens and are often activated by upstream plasma membrane leucine-rich repeat receptor-like kinases (LRR-RLKs). ERECTA (ER) is an LRR-RLK that regulates plant developmental processes through activating MAPK cascades. Tomato leaf curl Yunnan virus (TLCYnV) C4 protein interacts with BKI1, stabilizes it at the plasma membrane and impairs ER autophosphorylation through suppressing the dissociation of the BKI1/ER complex, and then inhibits the activation of downstream MAPK cascades, which ultimately creates a favorable environment for TLCYnV infection. This study provides a novel viral strategy to impair MAPK activation.