Genome-wide identification of ascorbate peroxidase (APX) gene family and the function of SmAPX2 under high temperature stress in eggplant

Ascorbate peroxidase (APX) plays pivotal roles in regulating diverse biological processes in plants against biotic and abiotic stresses by eliminating hydrogen peroxide (H2O2). However, the function and information of APX gene family members in eggplant's response to high temperature stress remain largely unclear. Herein, we have identified nine APXs in the eggplant genome (SmAPXs), which were classified into three clades and the members of each clade exhibited similar gene structures and motifs. SmAPXs were distributed on seven chromosomes and contained phytohormone responsiveness-, defense and stress-related, and transcription factors binding cis-elements within their promoters. Transcript expressions of some SmAPXs, especially SmAPX2 that localize in cytomembrane and cytoplasm, were up-regulated by high temperature and ABA treatment. SmAPX2 exhibits APX enzyme activity, which enables to catalyze oxidation of ascorbic acid by H2O2 in vitro and alleviate the H2O2 accumulation under high temperature stress by SmAPX2 transient expression in vivo. SmAPX2 silencing decreased eggplant's tolerance to high temperature stress, accompanied by transcript expression down-regulation of high temperature defense-related and ABA-response-related genes, reduction of APX enzyme activity, and increase of H2O2 content. These data provide comprehensive overview of SmAPX gene family, and indicate that SmAPX2 positively functions in eggplant response to high temperature stress.