Xu Li, Wang Jizong, Xiao Yu, Han Zhifu, Chai Jijie
Tsinghua-Peking Center for Life Sciences, Beijing Advanced Innovation Center for Structural Biology, Centre for Plant Biology, School of Life Sciences, Tsinghua University, Beijing, 100084, China.
Max Planck Institute for Plant Breeding Research, Cologne, 50829, Germany.
J Integr Plant Biol. 2023 Jan;65(1):235-248. doi: 10.1111/jipb.13279. Epub 2022 Jul 8.
Plants have developed innate immune systems to fight against pathogenic fungi by monitoring pathogenic signals known as pathogen-associated molecular patterns (PAMP) and have established endo symbiosis with arbuscular mycorrhizal (AM) fungi through recognition of mycorrhizal (Myc) factors. Chitin elicitor receptor kinase 1 of Oryza sativa subsp. Japonica (OsCERK1) plays a bifunctional role in mediating both chitin-triggered immunity and symbiotic relationships with AM fungi. However, it remains unclear whether OsCERK1 can directly recognize chitin molecules. In this study, we show that OsCERK1 binds to the chitin hexamer ((NAG) ) and tetramer ((NAG) ) directly and determine the crystal structure of the OsCERK1-(NAG) complex at 2 Å. The structure shows that one OsCERK1 is associated with one (NAG) . Upon recognition, chitin hexamer binds OsCERK1 by interacting with the shallow groove on the surface of LysM2. These structural findings, complemented by mutational analyses, demonstrate that LysM2 is crucial for recognition of both (NAG) and (NAG) . Altogether, these findings provide structural insights into the ability of OsCERK1 in chitin perception, which will lead to a better understanding of the role of OsCERK1 in mediating both immunity and symbiosis in rice.
植物通过监测被称为病原体相关分子模式（PAMP）的致病信号，发展出了先天免疫系统来对抗致病真菌，并通过识别菌根（Myc）因子与丛枝菌根（AM）真菌建立了共生关系。水稻亚种日本晴的几丁质激发子受体激酶1（OsCERK1）在介导几丁质触发的免疫反应以及与AM真菌的共生关系中发挥着双重功能。然而，OsCERK1是否能直接识别几丁质分子仍不清楚。在本研究中，我们表明OsCERK1直接与几丁质六聚体（（NAG）₆）和四聚体（（NAG）₄）结合，并确定了OsCERK1 - （NAG）₆复合物在2埃分辨率下的晶体结构。该结构显示一个OsCERK1与一个（NAG）₆相关联。识别时，几丁质六聚体通过与LysM2表面的浅沟相互作用结合OsCERK1。这些结构发现，辅以突变分析，表明LysM2对于识别（NAG）₆和（NAG）₄都至关重要。总之，这些发现为OsCERK1感知几丁质的能力提供了结构上的见解，这将有助于更好地理解OsCERK1在介导水稻免疫和共生中的作用。
