Genome-wide identification and functional analysis of PR4 genes reveal a JA–ScMYC2a–ScPR4-1 module in cold stress tolerance of jojoba (Simmondsia chinensis)

Jojoba ( Simmondsia chinensis ) is an important woody oil crop, but its cultivation is severely limited by extreme sensitivity to low temperatures. Pathogenesis-related protein 4 (PR4) genes participate in plant stress responses and are frequently associated with jasmonic acid (JA) signaling, but their functions in woody crops remain poorly understood. Here, six class II ScPR4 genes containing conserved Barwin-like domains were identified in jojoba. Phylogenetic and collinearity analyses revealed lineage-specific expansion of the family, mainly driven by tandem duplication. Among these genes, ScPR4–1 contained low-temperature- and MeJA-responsive cis-elements and was strongly induced by both treatments. Functional analyses in Arabidopsis , yeast, and jojoba hairy roots showed that ScPR4–1 enhanced cold tolerance by reducing ROS accumulation and membrane lipid peroxidation and promoting osmotic adjustment. Mechanistic studies further demonstrated that ScMYC2a directly bound to two G-box elements in the ScPR4–1 promoter and activated its transcription. DIECA treatment attenuated ScPR4–1 induction and partially weakened the protective effects of its overexpression, supporting the contribution of JA biosynthesis to this regulation. Together, these findings established a “JA– ScMYC2a – ScPR4–1 ” regulatory module underlying cold response in jojoba, providing novel insights and candidate targets for cold-tolerance improvement in woody crops.