A genome-wide analysis of ascorbate oxidase gene family and hormonal activity in mango exposed to enhanced UV-B radiation

Ascorbate oxidase (AO), an apoplastic enzyme from the multi-copper oxidase family, is vital in maintaining redox homeostasis, particularly under environmental stress conditions like enhanced UV-B radiation. Our research group has already reported that AO activity was inhibited under enhanced UV-B radiation stress, which may enhance the activity of ascorbate levels in mango fruit. Although the AO family has been studied in other crops, its role in Mangifera indica remains unexplored. This study conducted a comprehensive genome-wide analysis of the AO gene family in mango, which includes the identification and functional characterization of the AO family in the mango genome, including its structural features, regulatory elements, and expression patterns under enhanced UV-B radiation. A total of 19 MiAO gene family members were identified, each consisting of two to five exons, and they were distributed across 10 different chromosomes. Phylogenetic analysis showed a closed relationship of AO genes between mango and tomato, suggesting shared ancestry. Promoter analysis identified 21 cis-regulatory elements involved in several biological processes, including signalling, growth, phytohormone, development, and stress responses. Furthermore, hormonal analysis under UV-B indicated a significant reduction in MeJA, SA, and GA3 levels. However, the expression analysis demonstrated that MiAO5, MiAO6, MiAO7, MiAO8, and MiAO9 were significantly downregulated under enhanced UV-B radiation stress. These results indicated that hormone level reduction may positively regulate the expression of AO family member’s gene expression, which may increase the accumulation of ascorbic acid, resulting in ROS scavenging. These results shed light on MiAO’s role in mango under UV-B’s, offering a foundation for breeding UV-B-tolerant mangoes and refining cultivation techniques. Subsequent research will expand on this to pinpoint the specific contributions of individual MiAO genes.