Os<scp>CERK</scp>1 plays a crucial role in the lipopolysaccharide‐induced immune response of rice

<jats:title>Summary</jats:title><jats:p> <jats:list list-type="bullet"> <jats:list-item><jats:p>Plant cell surface receptor‐like kinases (<jats:styled-content style="fixed-case">RLK</jats:styled-content>s) mediate the signals from microbe‐associated molecular patterns (<jats:styled-content style="fixed-case">MAMP</jats:styled-content>s) that induce immune responses. Lipopolysaccharide (<jats:styled-content style="fixed-case">LPS</jats:styled-content>), the major constituent of the outer membrane of gram‐negative bacteria, is a common <jats:styled-content style="fixed-case">MAMP</jats:styled-content> perceived by animals and plants; however, the plant receptors/co‐receptors are unknown except for <jats:styled-content style="fixed-case">LORE</jats:styled-content>, a bulb‐type lectin S‐domain <jats:styled-content style="fixed-case">RLK</jats:styled-content> (B‐lectin <jats:styled-content style="fixed-case">SD</jats:styled-content>1‐<jats:styled-content style="fixed-case">RLK</jats:styled-content>) in Arabidopsis. Os<jats:styled-content style="fixed-case">CERK</jats:styled-content>1 is a multifunctional <jats:styled-content style="fixed-case">RLK</jats:styled-content> in rice that contains lysin motifs (LysMs) and is essential for the perception of chitin, a fungal <jats:styled-content style="fixed-case">MAMP</jats:styled-content>, and peptidoglycan, a bacterial <jats:styled-content style="fixed-case">MAMP</jats:styled-content>. Here, we analyzed the relevance of Os<jats:styled-content style="fixed-case">CERK</jats:styled-content>1 to <jats:styled-content style="fixed-case">LPS</jats:styled-content> perception in rice.</jats:p></jats:list-item> <jats:list-item><jats:p>Using <jats:italic>Os<jats:styled-content style="fixed-case">CERK</jats:styled-content>1</jats:italic>‐knockout mutants (<jats:italic>oscerk1</jats:italic>), we evaluated hydrogen peroxide (H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>) production and gene expression after <jats:styled-content style="fixed-case">LPS</jats:styled-content> treatment. We also examined the <jats:styled-content style="fixed-case">LPS</jats:styled-content> response in knockout mutants for the B‐lectin <jats:styled-content style="fixed-case">SD</jats:styled-content>1‐<jats:styled-content style="fixed-case">RLK</jats:styled-content> genes in rice and for all LysM‐protein genes in Arabidopsis.</jats:p></jats:list-item> <jats:list-item><jats:p>Compared with wild‐type rice cells, <jats:styled-content style="fixed-case">LPS</jats:styled-content> responses in <jats:italic>oscerk1</jats:italic> cells were mostly diminished. By contrast, rice lines mutated in either of three B‐lectin <jats:styled-content style="fixed-case">SD</jats:styled-content>1‐<jats:styled-content style="fixed-case">RLK</jats:styled-content> genes and Arabidopsis lines mutated in the LysM‐protein genes responded normally to <jats:styled-content style="fixed-case">LPS</jats:styled-content>.</jats:p></jats:list-item> <jats:list-item><jats:p>From these results, we conclude that Os<jats:styled-content style="fixed-case">CERK</jats:styled-content>1 is an <jats:styled-content style="fixed-case">LPS</jats:styled-content> receptor/co‐receptor and that the <jats:styled-content style="fixed-case">LPS</jats:styled-content> perception systems of rice and Arabidopsis are significantly different.</jats:p></jats:list-item> </jats:list> </jats:p>