Regulatory Mechanism Of The PpSEP1 (SEPALLATA) Gene During Fruit Ripening And Softening In Melting And Non-melting Peaches

SEPALLATA genes are members of a subfamily of MADS-box transcription factors,and have essential roles in floral organ development and fruit ripening.However,little is known about how PpSEP1 gene to control peach fruit ripening and softening.In this study,we used melting flesh cultivar(MF: ‘Jingchun' and ‘Shonghong')and non-melting flesh cultivar(NMF: ‘GeGu')fruits with differences in firmness and texture characteristics during ripening,and analyzed the patterns of PpSEP1 expression,ethylene biosynthesis and signal transduction,cell wall metabolism,and expression of other ripening-related genes.And In order to further discover the expression characteristics and possible function of the PpSEP1 gene in melting and non-melting peach fruits ripening and softening,PpSEP1 gene was silenced by virus-induced gene silencing(VIGS)to verify its function,and then we use yeast one-hybrid technology to demonstrate target genes of PpSEP1.The results are as following:1.In melting peaches,PpSEP1 could regulate fruit ripening and softening by directly involved in the process of ethylene synthesis and signal transduction,cell wall metabolism,N-glycan processing enzymemetabolism and so on.In non-melting peaches,PpSEP1 may affect the cell wall metabolism pathway to control the fruit ripening and softening.We speculated that PpSEP1 may regulate the process of the fruit ripening and softening through different ways in melting and non-melting peach cultivars.2.Virus-induced PpSEP1 gene silencing,transcriptional expression PpSEP1 was suppressed,fruit firmness was significantly higher than the control and ethylene production was also significantly inhibited.This indicated that fruit ripening was delayed.What's more,the expression of ripening and softening related genes like PpEIN2 ? PpEndo-PG ? PpLox1 were subject to varying degrees of inhibition during first 8 days of storageand PpACS2 ?PpPME1 were significantly inhibited during first 6 days.Whilethe expression of PpACO1?PpETR2 and Pp?-Hex2 were significantly inhibited at 6 d.However,transcription and expression PpPME3 and PpEXP2 was markedly suppressed at 0 d,and then their expressions were significantly higher than control fruits.Silence PpSEP1 delayed fruit ripening process,PpSEP1 transcription factor plays an important role in regulating the peach fruit ripening and softening.3.PpSEP1 CDs has two different fragments: PpSEP1 a and PpSEP1 b,but they are only different in AGC the three bases located in 183-186 bp,only a serine.And both of them exist in melting and non-melting peach fruits.What's more,the astonishing thing was that the ratio of PpSEP1b/PpSEP1 a in NMF was larger than MF.SEP transcription factor can probably bind with CArG-box motif in the promoter of downstream target genes.So we analyzed their3000 bp promoters upstream of the transcription start site and found that all of the examined genes had at least one typical CArG-box sequence.Yeast one-hybrid verification showed PpSEP1 a which contain serine sites may be combined with promoter of target genes PG.