Characterization and expression analysis of cDNAs encoding abscisic acid 8'-hydroxylase during mulberry fruit maturation and under stress conditions

Abscisic acid (ABA) 8'-hydroxylase is the key enzyme in the oxidative catabolism of ABA. CYP707A genes encode (+)-ABA 8'-hydroxylases that are involved in fruit ripening and abiotic stress responses. However, there are limited reports on the functions of CYP707A genes in mulberry. This study analyzed the transcriptional expression of CYP707A genes during fruit development and their response to exogenous ABA and uniconazole (UNI) treatment. Additionally, the expression patterns of CYP707A under stress conditions were explored in mulberry. We obtained six CYP707A gene (MnCYP707A1-MnCYP707A6) sequences from Morus notabilis genome database. Multiple sequence alignment results showed high conservation within the MnCYP707A genes. The expression profiles of these genes during fruit development and under stress conditions were analyzed by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). During fruit development, the expression levels of MaCYP707A1, MaCYP707A3, MaCYP707A5, and MaCYP707A6 were higher at the primary stage and then sharply declined to a lower level at the late stage. The expression of MaCYP707A1 in the fruit quickly declined at 1 d after 50 mmol/L UNI treatment. In addition, under Sodium chloride (NaCl) (0.3 % (w/v) at germination stage and 0.6 % (w/v) at seedling stage) or polyethylene glyco (PEG) 6000 (5 % (w/v) at germination stage and 20 % (w/v) at seedling stage) stress, most of the MaCYP707A genes were up-regulated, but displayed different patterns. Tissue-specific patterns of the CYP707A family appear to be universal under stress conditions. In a short, MaCYP707A genes play overlapping roles in ABA catabolism and MaCYP707A1 may be the key gene expressed during fruit maturation. Most of these genes were induced by abiotic stress, and various expression patterns were observed among the MaCYP707A in multiple mulberry tissues at different growth periods.