Proteomic analysis of leaf apoplast reveals that a jasmonate-regulated CHIA participates in the response to cold and drought stress in jojoba

Jojoba [Simmondsia chinensis (Link) Schneider] is sensitive to low temperatures, which hinders its cultivation in temperate arid regions. The apoplast is a cellular component outside the plasma membrane of plant cells and is widely involved in the response of plants to environmental stress. Here, we used the infiltration-centrifugation method to extract apoplast fluid from jojoba leaves and analyzed changes in the apoplast proteome after cold acclimation using quantitative proteomics. In total, 751 apoplast proteins were identified in jojoba, and the abundance of 200 proteins showed significant changes after cold acclimation. These proteins were primarily involved in defense, cell wall modification, carbohydrate metabolism, and redox balance. We also investigated the function and regulation of a cold acclimation-responsive class Ⅲ chitinase ScCHIA. The results showed that the overexpression of ScCHIA enhanced the tolerance of Arabidopsis, yeast, and jojoba to low temperature and osmotic stress. Under cold stress, ScCHIA-overexpressing Arabidopsis accumulated more osmolytes, activated antioxidant enzymes, and reduced stomatal aperture size, which may contribute to enhanced tolerance to cold stress. ScCHIA was induced by methyl jasmonate (MeJA) application, and electrophoretic mobility shift assay (EMSA), yeast one-hybrid (Y1H), and luciferase activity assays demonstrated that an E-box cis-acting element on the ScCHIA gene promoter mediated regulation of ScCHIA by MeJA signaling, indicating that elevated levels of MeJA caused by cold acclimation may promote the expression of ScCHIA, thereby enhancing the cold tolerance of jojoba. Our research highlights the important role of the apoplast in plant response to low temperature stress and improves the understanding of the functions and regulatory mechanisms of plant chitinases in abiotic stress response.