OsMKK6 Regulates Disease Resistance in Rice.

Mitogen-activated protein kinase cascades play important roles in various biological programs in plants, including immune responses, but the underlying mechanisms remain elusive. Here, we identified the lesion mimic mutant () and determined that the mutant harbored a loss-of-function allele for . developed reddish-brown spots on its leaves at the heading stage, as well as on husks. Compared to the wild type, the mutant exhibited enhanced resistance to the fungal pathogen () and to the bacterial pathogen pv. (). OsMKK6 interacted with OsMPK4 (MITOGEN-ACTIVATED KINASE 4) in vivo, and OsMKK6 phosphorylated OsMPK4 in vitro. The mutant is also a lesion mimic mutant, with reddish-brown spots on its leaves and husks. Pathogen-related genes were significantly upregulated in , and this mutant exhibited enhanced resistance to compared to the wild type. Our results indicate that OsMKK6 and OsMPK4 form a cascade that regulates immune responses in rice.