摘要Rapid alkalinization factors(RALFs)in plants have been reported to dampen pathogen-associated molecular pattern(PAMP)-triggered immunity via suppressing PAMP-induced com-plex formation between the pattern recognition receptor(PRR)and its co-receptor BAK1.How-ever,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 Scle-rotinia sclerotiorum in a FERONIA(FER)-dependent manner.LORELEI(LRE)-like glycosylphosphati-dylinositol(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 ter-minus of RALFs abolished,while the constitutive formation of two disulfide bridges between these cysteines promoted the RALF22-elicited ROS pro-duction and resistance against S.sclerotiorum,demonstrating the requirement of these cysteines in the functions of RALF22 in plant immunity.Fur-thermore,RALF22 amplified the Pep3-induced im-mune signal by dramatically increasing the abun-dance of PROPEP3 transcript and protein.Supply with RALF22 induced resistance against S.scle-rotiorum in Brassica crop plants.Collectively,our results reveal that RALF22 triggers immune re-sponses 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.