An apoplastic peptide activates salicylic acid signalling in maize

Localized control (局部控制) of cell death is crucial for the resistance of plants to pathogens. Papain-like cysteine proteases (PLCPs; 类木瓜半胱氨酸蛋白酶) regulate plant defence to drive cell death and protection against biotrophic pathogens (活体营养的病原菌). In maize (Zea mays), PLCPs are crucial in the orchestration of salicylic acid (SA)-dependent defence signalling. Despite this central role in immunity, it remains unknown how PLCPs are activated, and which downstream signals they induce to trigger plant immunity. Here, we discover an immune signalling peptide, Z. mays immune signalling peptide 1 (Zip1), which is produced after salicylic acid (SA) treatment. In vitro studies demonstrate that PLCPs are required to release bioactive Zip1 from its propeptide (前肽) precursor. Conversely, Zip1 treatment strongly elicits SA accumulation in leaves. Moreover, transcriptome analyses revealed that Zip1 and SA induce highly overlapping transcriptional changes. Consequently, Zip1 promotes the infection of the necrotrophic (死体营养的) fungus Botrytis cinerea (灰霉病), while it reduces virulence (毒性) of the biotrophic fungus Ustilago maydis (黑粉菌). Thus, Zip1 represents the previously missing signal that is released by PLCPs to activate SA defence signalling.

细胞死亡的局部控制对于植物对病原菌抗性至关重要。类木瓜半胱氨酸蛋白酶PLCP调控植物抗性以驱动细胞死亡并保护植物免受活体营养病原菌的侵染。在玉米中，PLCP在依赖于水杨酸的抗性信号转导中扮演重要角色。除了PLCP在植物免疫中的重要作用，对于PLCP是如何被激活，以及其诱导的哪些下游信号以激活植物免疫反应还不清楚。本文发现了一个免疫信号多肽Zip1，该多肽在水杨酸SA处理后在植物体内出现。体外试验表明由多肽前体到具有生物活性的Zip1需要PLCP的存在。相反，Zip1处理促进了SA在植物叶片中的积累。此外，转录组分析显示Zip1和SA诱导的转录改变在很大程度上一致。Zip1促进死体营养病原灰霉病的侵染，但其能减少活体营养病原黑粉菌的毒性。因此，本文的研究报道了在先前一直被忽视的由PLCP释放的Zip1激活SA抗性信号转导。

通讯：Gunther Doehlemann (http://www.ag-doehlemann.botanik.uni-koeln.de/1869.html)

个人简介：1998-2003年，凯泽斯劳滕大学，微生物学、植物病理学学士；2003-2006年，凯泽斯劳滕大学，植物病理学博士；2006-2008年，马克斯普朗克陆地微生物学研究所，博士后。

doi: 10.1038/s41477-018-0116-y