The plant apoplast, which serves as the frontline battleground for long-term host–pathogen interactions, harbors a wealth of disease resistance resources. However, the identification of the disease resistance proteins in the apoplast is relatively lacking. In this study, we identified and characterized the rice secretory protein OsSSP1 ( secretory small protein 1). OsSSP1 can be secreted into the plant apoplast, and either treatment of recombinant OsSSP1 or overexpression of in rice could trigger plant immune response. The expression of is suppressed significantly during infection in the susceptible rice variety Taibei 309, and -overexpressing lines all show strong resistance to . Combining the knockout and overexpression results, we found that OsSSP1 positively regulates plant immunity in response to fungal infection. Moreover, the recognition and immune response triggered by OsSSP1 depend on an uncharacterized transmembrane OsSSR1 (secretory small protein receptor 1) and the key co-receptor OsBAK1, since most of the induced immune response and resistance are lost in the absence of or . Intriguingly, the OsSSP1 protein is relatively stable and can still induce plant resistance after 1 week of storage in the open environment, and exogenous OsSSP1 treatment for a 2-week period did not affect rice yield. Collectively, our study reveals that OsSSP1 can be secreted into the apoplast and percepted by OsSSR1 and OsBAK1 during fungal infection, thereby triggering the immune response to enhance plant resistance to . These findings provide novel resources and potential strategies for crop breeding and disease control.

中文翻译：

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膜受体 OsSSR1 和辅助受体 OsBAK1 对诱导型分泌性小蛋白 OsSSP1 的识别赋予水稻对稻瘟病菌的抗性

植物质外体是宿主与病原体长期相互作用的前线战场，蕴藏着丰富的抗病资源。然而，质外体中抗病蛋白的鉴定相对缺乏。在本研究中，我们鉴定并表征了水稻分泌蛋白 OsSSP1（分泌小蛋白 1）。 OsSSP1可以分泌到植物质外体中，重组OsSSP1的处理或在水稻中的过度表达都可以触发植物免疫反应。在感病水稻品种台北309感染过程中，β的表达受到显着抑制，过表达株系均表现出较强的抗性。结合敲除和过表达结果，我们发现OsSSP1积极调节植物应对真菌感染的免疫。此外，OsSSP1 触发的识别和免疫反应依赖于未表征的跨膜 OsSSR1（分泌性小蛋白受体 1）和关键的辅助受体 OsBAK1，因为大多数诱导的免疫反应和抵抗力在缺乏或不存在的情况下会丢失。有趣的是，OsSSP1蛋白相对稳定，在开放环境中储存1周后仍然可以诱导植物抗性，并且外源OsSSP1处理2周并没有影响水稻产量。总的来说，我们的研究表明，在真菌感染过程中，OsSSP1 可以分泌到质外体中，并被 OsSSR1 和 OsBAK1 感知，从而触发免疫反应，增强植物的抗性。这些发现为作物育种和疾病控制提供了新的资源和潜在的策略。