Key Laboratory of Biology of Crop Pathogens and Insects of Zhejiang Province, Institute of Biotechnology, College of Agriculture and Biotechnology, Zhejiang University, 866 Yu Hang Tang Road, Hangzhou, 310058, China.
Centre of Analysis and Measurement, Zhejiang University, 866 Yu Hang Tang Road, Hangzhou, 310058, China.
J Integr Plant Biol. 2023 Nov;65(11):2519-2534. doi: 10.1111/jipb.13566. Epub 2023 Oct 25.
Rapid alkalinization factors (RALFs) in plants have been reported to dampen pathogen-associated molecular pattern (PAMP)-triggered immunity via suppressing PAMP-induced complex formation between the pattern recognition receptor (PRR) and its co-receptor BAK1. However, the direct and positive role of RALFs in plant immunity remains largely unknown. Herein, we report the direct and positive roles of a typical RALF, RALF22, in plant immunity. RALF22 alone directly elicited a variety of typical immune responses and triggered resistance against the devastating necrotrophic fungal pathogen Sclerotinia sclerotiorum in a FERONIA (FER)-dependent manner. LORELEI (LRE)-like glycosylphosphatidylinositol (GPI)-anchored protein 1 (LLG1) and NADPH oxidase RBOHD were required for RALF22-elicited reactive oxygen species (ROS) generation. The mutation of cysteines conserved in the C terminus of RALFs abolished, while the constitutive formation of two disulfide bridges between these cysteines promoted the RALF22-elicited ROS production and resistance against S. sclerotiorum, demonstrating the requirement of these cysteines in the functions of RALF22 in plant immunity. Furthermore, RALF22 amplified the Pep3-induced immune signal by dramatically increasing the abundance of PROPEP3 transcript and protein. Supply with RALF22 induced resistance against S. sclerotiorum in Brassica crop plants. Collectively, our results reveal that RALF22 triggers immune responses and augments the Pep3-induced immune signal in a FER-dependent manner, and exhibits the potential to be exploited as an immune elicitor in crop protection.
植物中的快速碱化因子（RALFs）已被报道通过抑制模式识别受体（PRR）与其共受体 BAK1 之间的病原体相关分子模式（PAMP）诱导的复合物形成来抑制 PAMP 触发的免疫。然而，RALFs 在植物免疫中的直接和积极作用在很大程度上仍然未知。在此，我们报告了一种典型的 RALF，RALF22，在植物免疫中的直接和积极作用。RALF22 单独直接引发了各种典型的免疫反应，并以 FERONIA（FER）依赖的方式引发了对破坏性坏死真菌病原体核盘菌的抗性。LORELEI（LRE）样糖基磷脂酰肌醇（GPI）锚定蛋白 1（LLG1）和 NADPH 氧化酶 RBOHD 是 RALF22 诱导活性氧（ROS）产生所必需的。在 RALF 末端保守半胱氨酸的突变消除了，而这些半胱氨酸之间的两个二硫键的组成形成促进了 RALF22 诱导的 ROS 产生和对核盘菌的抗性，表明这些半胱氨酸在 RALF22 在植物免疫中的功能中是必需的。此外，RALF22 通过显著增加 PROPEP3 转录本和蛋白的丰度来放大 Pep3 诱导的免疫信号。RALF22 的供应在十字花科作物植物中引发了对核盘菌的抗性。总之，我们的结果表明，RALF22 以 FER 依赖的方式触发免疫反应并增强 Pep3 诱导的免疫信号，并显示出作为作物保护中免疫诱导剂的潜力。
