Characterization and expression of abscisic acid signal transduction genes during mulberry fruit ripening

The plant hormone abscisic acid (ABA) plays an important role in fruit development. To analyze the transcriptional regulation of ABA signaling pathway-related genes during mulberry (Morus alba L.) fruit development and ripening, 17 genes participating in ABA signal transduction were isolated from the Morus notabilis genome database, including five MnPYL, six MnPP2C, and six MnSnRK2 genes. The result of multiple sequence alignment revealed that their functional amino acid residues and domains are conserved within each gene family. The expression profiles of ABA signaling pathway-related genes in the fruit of Morus atropurpurea cv. Jialing No. 40 were measured by quantitative real-time polymerase chain reaction. The transcripts of MaPYL4, MaPP2C5, and MaSnRK2.6 were expressed at a relatively higher level during the entire development process. Moreover, the transcript levels of MaPYL1/3/5, MaPP2C2/4/5/6, and MaSnRK2.3/2.6 were lower during the early-maturation stage and higher during the post-maturation stage, which suggests that they may play a vital role in regulating mulberry fruit ripening. In addition, these genes showed strong responses to exogenous ABA, fluridone, glucose, and sucrose. This study also indicated that exogenous ABA, sucrose, and glucose may promote fruit maturity, while fluridone significantly inhibits fruit ripening.