Study On Effects Of Abscisic Acid And Methyl Jasmonate On The Regulation Of Tomato Fruit Ripening And Related MiRNA Involved

Tomato fruit ripening is a complex and precisely regulated process.The plant hormones abscisic acid(ABA)and methyl jasmonate(MeJA)play important roles in regulating tomato ripening.In this research,cherry tomato(Solamum lycopersicum L cv Xin Taiyang)was used as the material.The effect of ABA and MeJA on tomato ripening was analyzed,as well as the effect of ABA on the primary metabolite components,the bioactive compounds and antioxidant activities in tomato fruit.Also,the effect of MeJA on ethylene metabolism during tomato ripening were analyzed The related regulatory miRNAs involved in tomato ripening were identified by small RNA sequencing and degradation sequencing analysis.The results showed as follows1.Exogenous ABA accelerated postharvest ripening process of tomato and enhanced the relative levels of some primary metabolites.The expressions of most key genes associated with metabolomics were stimulated(log2 fold change=1.06 to 3.64)by exogenous ABA during tomato ripening,which may promote the related enzymatic activities,thus enhancing the relative levels of some primary metabolites,such as glucose(3.05-fold),lyxose(2.64-fold)and fructose(3.25-fold),citric acid(2.99-fold),citramalic acid(1.80-fold),ascorbic acid(1.70-fold)and gluconic acid(1.70-fold),as well as serine(1.91-fold),pyroglutamic acid(1.93-fold),GABA(1.90-fold),glutamic acid(2.60-fold),aspartic acid(2.16-fold),asparagine(1.72-fold)and glutamine(1.69-fold).These results indicate ABA is systematically involved in the expression of related genes and the regulation of primary metabolites,which may be a useful regulation target to improve tomato taste and flavor2.Exogenous ABA activated the phenylpropanoid pathway and improved bioactive components and antioxidant capacities of tomato during postharvest ripening.The results of the present study indicated that exogenous ABA treatment induced the expressions of PAL1,C4H,4CL2,CHS2,F3H,and FLS(1.13-to 26.95-fold);promoted PAL,POD,and PPO activities;accelerated the accumulation of total phenolics,total flavonoids,and phenolic compounds;and enhanced lycopene and ascorbic acid contents,as well as the antioxidant enzymatic activities(CAT and APX)and antioxidant capacities(FRAP and DPPH)during tomato ripening3.The results showed that a significant acceleration in ripening in MeJA-treated fruit was observed,along with the accelerated changes of fruit colour and firmness The expression levels of the genes associated with ethylene biosynthesis and most of the ethylene signal transduction were up-regulated after exogenous MeJA application Meanwhile,the expressions of ACS and ACO were up-regulated,and ACS and ACO activities as well as ethylene production were enhanced.The expression levels of ETR3,ETR4,ETR6,EIN2,EIL2,EIL3,EIL4 and ERF1 were up-regulated by MeJA during tomato ripening.The expression level of CTR1,however,was down-regulated Moreover,the expression level of EIL1 was positively regulated at the early ripening stage whereas negatively regulated at the late ripening stage,whereas the expressions of CTR3 and CTR4 showed the opposite expression patterns.MeJA treatment had no significant effect on the expressions of ETR1 and ETR2 during tomato ripening Results showing the increase of ethylene production,response and action,would be one of the major mechanisms of MeJA in accelerating postharvest tomato ripening4.Exogenous MeJA can up-regulate the expressions of the major genes(PAL1,C4H,4CL2,CHS2,CHI,F3H,and FLS)involved in the phenylpropanoid pathway,and enhance the enzymatic activities(PAL,C4H,4CL,CHS,and CHI)associated with the phenylpropanoid pathway,thereby accelerating the accumulations of total phenolics and flavonoids contents,as well as increasing the contents of most phenolic compounds during tomato ripening5.The sequencing analysis identified 63 conserved miRNAs and 16 novel miRNAs which were differentially regulated during tomato ripening,among which 27 conserved miRNAs and 6 novel miRNAs were differentially expressed in response to ABA/NDGA.Degradation sequencing identified target genes of 54 conserved miRNAs and 13 novel miRNAs.Through GO and KEGG enrichment analysis of miRNA target genes,it was found that the miRNA target genes in this research mainly participate in the processes of plant hormone signal transduction,transcriptional regulation,RNA synthesis and degradation and substance synthesis,suggesting that miRNA may regulate the ripening process of tomato by controlling the expressions of target genes associated with hormone signal transduction and interaction,as well as RNA homeostasis and substance synthesis.