The Roles Of S1MYC2 And Its Relationships With Arginine Metabolism In MeJA-Induced Chilling Resistance Of Postharvest Tomato Fruit

Jasmonic acid（JA）and methyl jasmonate（MeJA）are endogenous signaling molecules and play important roles in the control of postharvest chilling injury of various fruits and vegetables.MYC2 is the master regulator in JA signaling pathway and involves in JA-induced defense responses of many fruits and vegetables.But,the roles of SlMYC2 in MeJA-induced chilling tolerance of postharvest fruits are far from being clearly understood.Arginine is a precursor for synthesis of nitric oxide（NO）and polyamines.Previous studies pointed out that MeJA treatment could promote arginine metabolism,however,the mechanism of MeJA-induced arginine metabolism need further study.Fruit tomato was used as a material for study of postharvest chilling,and established SlMYC2-silenced tomato fruit by virus-induced gene silence（VIGS）and the fruits were treated with MeJA before cold storage.The indexes correlated with fruit chilling tolerance and arginine metabolism were assayed.Moreover,we preliminarily identified SlMYC2-target genes of arginine metabolism by electrophoretic mobility shift assay（EMSA）.The main results were as follows:（1）In the present work,the gene of transcription factor SlMYC2 in tomato fruit was silenced by tobacco rattle virus-mediated VIGS technique,and the expression level of SlMYC2was measured by semi-quantitative PCR and quantitative real-time PCR.Compared with non-silenced fruit,SlMYC2 expression level in SlMYC2-silenced tomato fruit was reduced by83%.These results indicated that the SlMYC2-silenced tomato fruits were successfully constructed;（2）Before cold storage,the tomato fruits including control and SlMYC2-silenced fruit were treated with 0.05 mmol L^-1 MeJA.These results indicated that MeJA treatment markedly increased total phenolic content,lycopene content and antioxidant enzyme activities,including superoxide dismutase,peroxidase,catalase,and ascorbate peroxidase;inhibited the increase of electrical conductivity and malondialdehyde content;induced the expression levels of cold resistance related genes,such as SlICE1,SlICE1a,SlCBF1 and SlCOR,and effectively reduced the chilling injury incidence and chilling injury index;（3）The silence of SlMYC2 aggravated the occurrence of chilling injury,and significantly inhibited the inductive effects of MeJA on antioxidant enzymes activities,lycopene content,total phenolic content and expression levels of cold resistance related genes in tomato fruit,which indicated that SlMYC2 might play positive regulatory roles in MeJA-induced tomato fruit chilling tolerance;（4）The treatment with MeJA enhanced the expression levels of genes（SlARG1,SlARG2,SlADC,SlODC and SlOAT）encoding the enzymes related arginine metabolism,promoted the accumulation of glutamate,proline,putrescine,spermine and spermidine;however,the silence of SlMYC2 also significantly counteracted the effects of MeJA on arginine metabolism;（5）The prokaryotic expression vector of pET-28a-SlMYC2 was successfully constructed and the purified SlMYC2 protein was obtained;（6）EMSA results indicated that the target genes of SlMYC2 regulating arginine metabolism might be SlARG1,SlARG2 and SlODC in tomato fruit.