Characteristics and regulatory pathway of the PrupeSEP1 SEPALLATA gene during ripening and softening in peach fruits.

SEPALLATA genes are members of a subfamily of MADS-box transcription factors, and have essential roles in floral organ development and fruit ripening. In this study, the PrupeSEP1 gene was cloned from peach flesh. Its deduced amino acid sequence was very similar to that of MdMADS8 and MdMADS9 in apple and MADS-RIN-like in strawberry. During storage of melting flesh (MF) peach, the pattern of SEP1 expression was similar to that of ethylene biosynthesis and ethylene signal transduction-related gene expression (EIN2 and ETR2). The SEP1 expression level was correlated with that of EIN2 and ETR2. Furthermore, in MF, cell wall modification-related genes (Endo-PG3, EXP2 and PME3), N-glycan processing genes (β-Hex2 and α-Man) and Lox1 exhibited similar expression patterns to that of SEP1. However, in non-melting flesh (NMF) peach, the SEP1 expression pattern was different from that of MF peach. Moreover, in NMF, only EXP2, LOX1, and α-Man expression patterns were similar to that of SEP1. After SEP1 expression was inhibited by virus-induced gene silencing technique (VIGS) in MF peach, compared with the control, the fruit remained firm and fruit softening was delayed. While expression levels of the ripening and softening related genes, ACS2, EIN2, PME1, Endo-PG3, ACO1, ETR2,β-Hex2 and Lox1, were significantly decreased in SEP1-silenced peach, the transcription of EXP2 and PME3 were significantly enhanced except at the harvest stage. Yeast one-hybrid verification showed SEP1 can interact with promoter of target genes PGs. Our results indicate SEP1 may regulate fruit ripening and softening of MF peaches, while this regulation may be lost in the NMF peaches.