Overexpressed BSR1 -Mediated Enhancement of Disease Resistance Depends on the MAMP-Recognition System.

Plant plasma membrane-localized receptors recognize microbe-associated molecular patterns (MAMPs) and activate immune responses via various signaling pathways. Receptor-like cytoplasmic kinases (RLCKs) are considered key signaling factors in plant immunity. BROAD-SPECTRUM RESISTANCE 1 (BSR1), a rice RLCK, plays a significant role in disease resistance. Overexpression ofBSR1confers strong resistance against fungal and bacterial pathogens. Our recent study revealed that MAMP-triggered immune responses are mediated by BSR1 in wild-type rice and are hyperactivated inBSR1-overexpressing rice. It was suggested that hyperactivated immune responses were responsible for the enhancement of broad-spectrum disease resistance; however, this remained to be experimentally validated. In this study, we verified the above hypothesis by disrupting the MAMP-recognition system in BSR1-overexpressing rice. To this end, we knocked outOsCERK1, which encodes a well-characterized MAMP-receptor-like protein kinase. In the background of BSR1 overaccumulation, the knockout ofOsCERK1nearly abolished the enhancement of blast resistance. This finding indicates that overexpressedBSR1-mediated enhancement of disease resistance depends on the MAMP-triggered immune system, corroborating our previously suggested model.