Characterization and Expression Analysis of Early Drought-Induced MaAPX Gene in Mulberry

Mulberry tree ( Morus alba ) has a wide ecological distribution attributed to its strong adaptability and is also an important perennial economic tree species. However, the molecular mechanisms responsible for its adaptability remain unknown. Ascorbate peroxidase (APX) is a key antioxidant enzyme that defends against oxidative damage in plants under various stresses. In this study, the abundance of mulberry APX (MaAPX) in leaves was upregulated under drought stress. MaAPX, located in the cytoplasmic membrane and nucleus, is a transmembrane hydrophilic protein that is not a secretory signaling protein and can be phosphorylated. The full-length of its coding gene, MaAPX , is 750 bp. The expression of MaAPX changed with natural light and seasons under field condition and varied among mulberry cultivars and was not related to genome duplication. MaAPX expression in leaves and roots was influenced by many abiotic stress and exogenous hormones treatments. Under heat and NaCl stress, it was downregulated in leaves but upregulated in roots. Under drought stress, MaAPX expression was upregulated in both leaves and roots. Under ethylene and ABA treatment, MaAPX expression decreased in leaves but increased in roots. Under salicylic acid treatment, it slightly decreased in both leaves and roots. Our work provides a comprehensive analysis of the expression on MaAPX , which lays a foundation for further MaAPX function exploration and genetic application research in mulberry.