Transcriptional regulation of PaPYLs, PaPP2Cs and PaSnRK2s during sweet cherry fruit development and in response to abscisic acid and auxin at onset of fruit ripening

To further understand the basis of abscisic acid (ABA) signal transduction in regulating sweet cherry fruit development and ripening, and also the interaction between ABA and indole acetic acid (IAA) at the onset of fruit ripening, full-length or partial cDNA of three PaPYLs (ABA receptor), six PaPP2Cs (type 2C protein phosphatase) and six PaSnRK2s (subfamily 2 of SNF1-related kinases) were identified from sweet cherry. Multiple alignments and phylogeny analyses showed that most of the functional residues or domains were well conserved within each gene family; all PaPP2Cs belonged to the group A PP2C; PaSnRK2.4 and PaSnRK2.5 belonged to subclass III of SnRK2. PaPYL2/3, PaPP2C3/4/6 and PaSnRK2.4 were highly expressed at the early stages of fruit development. Moreover, PaPYL2, PaPP2C3/4, PaSnRK2.4 also had a high expression level at the onset of fruit ripening. Exogenous ABA treatment at 28 days after full bloom decreased the IAA level and promoted fruit ripening by increasing anthocyanin and soluble solids content. However, although IAA treatment induced the ABA accumulation, it delayed the onset of fruit ripening. Most of the PaPYLs and PaSnRK2s didn't strongly respond to ABA and IAA treatments at 28 days after full bloom, while expressions of PaPP2C3, PaPP2C5 and PaPP2C6 were significantly induced by exogenous ABA and PaPYL1 was significantly induced by exogenous IAA.