Study On The Epigenetic Mechanism Of Sly-miR159 Regulating Postharvest Senescence Of Tomato Fruit

miRNAs play an irreplaceable role in affecting growth of plant,ripening and senescence of fruit.Studying the effects of miRNAs on tomato growthgrowth,ripening and senescence of fruit could provide new ideas for understanding the epigenetic senescence regulation mechanism of plants.The research on the mechanism of postharvest senescence is of great significance for fruit storage and circulation.In this study,the STTM-miR159 and miR159 overexpression transgenic tomato plant system was constructed through STTM(short tandem target mimic)and transgenic engineering technology.The functions of miR159 and the target gene ACS8 in tomato growth,development,ripening and senescence were explored,and the regulation mechanism of miR159 on tomato fruit ripening and senescence was revealed.The main results are as follows:(1)The expression levels of miR159 and target gene ACS8 during tomato fruit development was analyzed,and it was found that the expression levels of miR159 and target gene ACS8 in tomato floral organs,fruit young fruit development and fruit sepals were negatively correlated.The STTM-miR159 transgenic tomato had an inhibitory effect on the expansion and development of young fruit,the number and density of peel cells,the thickness of the sepals were reduced.The miR159 overexpression transgenic lines promoted the development of young tomato fruit,the fruit ovary expanded beforehand without pollination,and the thickness of the pericarp was increased.The fruit produced was parthenocarpy without fertile seeds.It showed that the expression levels of miR159 and target gene ACS8 were involved in the growth and development process of tomato fruit.(2)miR159 and the target gene ACS8 were involved in the regulation of fruit preharvest ripening.The STTM-miR159 and miR159 overexpression transgenic tomato plants had advanced the time from flowering to color breaking.The average fruit color breaking time of STTM-miR159 and miR159 overexpression transgenic tomato plants are 34 dpa and 27 dpa,respectively.Compared with the wild type,the STTM-miR159 transgenic lines delayed the process from color breaking to red ripening of tomato fruit,the miR159 overexpression transgenic lines promoted the process from color breaking to red ripening of tomato fruit.It showed that while miR159 was disturbed or overexpressed,it would affect the color breaking time of the fruit.It indicating that the regulation of miR159 and the target gene ACS8 affected the preharvest ripening of tomato fruit.(3)miR159 and target gene ACS8 were involved in the postharvest ripening and senescence process of tomato fruit.The STTM-miR159 transgenic lines significantly delayed the ripening and senescence of postharvest tomato fruit,inhibited the ethylene release rate of tomato fruit during postharvest storage,and affected the expression of downstream related genes in the ethylene signal transduction pathway.Overexpression of the miR159 transgenic lines significantly shortened the time from color breaking to red ripening in postharvest tomato fruit,increased the rate of ethylene production of postharvest fruit,down-regulated the expression level of CTR1 and up-regulated the expression levels of ETR4,EIN2,EIL3 and ERF1 genes in the ethylene signal pathway.The up-regulation of ERF1 gene was the most significant.It indicated that the regulation of the target gene ACS8 by miR159 affected the ethylene signal transduction pathway,which in turn affected the ripening and senescence of postharvest tomato fruit.In addition,miR159 and the target gene ACS8 also affected the changes of nutrients in postharvest tomato fruit.In summary,the regulation of the target gene ACS8 by miR159 was involved in the growth,development,ripening and senescence process of tomato fruit.This study provided a basis for the research of the mechanism of miR159 regulating fruit ripening and senescence.