RALF22 promotes plant immunity and amplifies the Pep3 immune signal

• Published in: Journal of integrative plant biology Vol. 65; no. 11; pp. 2519 - 2534
• Main Authors: He, Yu‐Han, Chen, Song‐Yu, Chen, Xing‐Yan, Xu, You‐Ping, Liang, Yan, Cai, Xin‐Zhong
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.11.2023; 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%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; Hainan Institute,Zhejiang University,Sanya 572025,China
• Subjects: Amplification; C-Terminus; Complex formation; FER; Glycosylphosphatidylinositol; Immune response; NAD(P)H oxidase; Pathogens; Pattern recognition; Pattern recognition receptors; Pep3; Plant immunity; Plant protection; Proteins; RALF22; Reactive oxygen species; Receptors; Sclerotinia sclerotiorum; Sclerotinia sclerotiorum; FER; RALF22; Pep3; plant immunity; reactive oxygen species
• ISSN: 1672-9072; 1744-7909
• DOI: 10.1111/jipb.13566

ABSTRACT 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. The rapid alkalinization factor RALF22 elicits plant immunity and augments Pep3‐induced immune signals, providing a paradigm of synergistic promotion of plant immunity by two phytocytokines and suggesting RALF22 as an immune elicitor for potential use in crop protection.