Abstract：
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 (Oryza sativa secretory small protein 1). OsSSP1 can be secreted into the plant apoplast, and either in vitro treatment of recombinant OsSSP1 or overexpression of OsSSP1 in rice could trigger plant immune response. The expression of OsSSP1 is suppressed significantly during Magnaporthe oryzae infection in the susceptible rice variety Taibei 309, and OsSSP1-overexpressing lines all show strong resistance to M. oryzae. 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 OsSSR1 or OsBAK1. 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 M. oryzae. These findings provide novel resources and potential strategies for crop breeding and disease control.
摘要：
植物原生质体，作为长期宿主-病原体相互作用的前线战场，拥有丰富的抗病资源。然而,在质外体中鉴定这些抗病蛋白是相对缺乏的。在这项研究中,我们确定了水稻分泌蛋白OsSSP1（水稻分泌小蛋白1）。OsSSP1蛋白可以分泌到植物质外体,水稻的体外处理和过表达都可以触发植物的免疫反应。在易感水稻TP309的稻瘟病菌感染过程中，OsSSP1的表达受到显着抑制，OsSSP1过表达的品系均对米曲霉表现出较强的抗性。结合敲除和过表达结果，我们发现OsSSP1在真菌感染时积极调节植物免疫。此外，由OsSSSP1触发的识别和免疫应答依赖于未表征的跨膜OsSSR1(分泌性小蛋白受体1)和关键的共受体OsBAK1,因为大多数诱导的免疫应答和抗性在OsSSR1或OsBAK1缺失的情况下丧失。此外，OsSSP1蛋白相对稳定，在开放环境中储存一周后仍能诱导植物抗性，外源OsSSP1处理2周不影响水稻产量。一起,我们的数据表明，在真菌感染期间，OsSSSP1蛋白被分泌到质外体中，并被质膜受体OsSSR1和OsBAK1接受，随后引发免疫反应以增强植物对米曲霉的抗性，为作物育种和绿色病虫害防治提供新的资源和线索。
