Abstract
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 of BSR1 confers 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 in BSR1-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 out OsCERK1, which encodes a well-characterized MAMP-receptor-like protein kinase. In the background of BSR1 overaccumulation, the knockout of OsCERK1 nearly abolished the enhancement of blast resistance. This finding indicates that overexpressed BSR1-mediated enhancement of disease resistance depends on the MAMP-triggered immune system, corroborating our previously suggested model.
Highlights
Plants can detect approaching microbes by recognizing microbe-associated molecular patterns (MAMPs), and in response activate various immune responses, which are referred to as pattern-triggered immunity (PTI) [1]
We attempted to knock out OsCERK1 in a BROAD-SPECTRUM RESISTANCE 1 (BSR1)-overexpressing line using the CRISPR/Cas9 system [18]
It was suggested that BSR1-overexpressing rice might be resistant to Agrobacterium infection, as it is resistant to the bacterial pathogens X. oryzae pv. oryzae and Burkholderia glumae [7]
Summary
Plants can detect approaching microbes by recognizing microbe-associated molecular patterns (MAMPs), and in response activate various immune responses, which are referred to as pattern-triggered immunity (PTI) [1]. PTI acts as a barrier to a broad spectrum of indigenous microbial species. Receptor-like kinases (RLKs) and receptor-like proteins on the plasma membrane form pattern-recognition receptor complexes to perceive MAMPs and activate intracellular signaling pathways [2]. Activated signaling factors regulate downstream responses, such as the production of reactive oxygen species (ROS) and the transcriptional activation of defense-related genes, followed by signal transduction via plant hormones and phytoalexin biosynthesis [1,3,4]. Virulent microbes (i.e., pathogens) have evolved various means to avoid triggering PTI in host plants, including the secretion of effectors and structural variations of MAMPs [5]
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