Effect Of MeJA On Cold-resistance And Cold Stress Of TACOI1/TaMYC2 Gene In Winter Wheat

Wheat is one of the major sources of grain in China.One of the major abiotic stress factors—low temperature,which severely limits the distribution and productivity of wheat.Dongnongdongmai 1(Dn1)is the first winter wheat variety capable of safely wintering in the highcold areas of Heilongjiang Province(tolerant to low temperature of-30°C),its returning rate is more than 85%.Plant hormones are important signaling molecules and play an important role in plant abiotic stress.We have constructed the mic RNA library of tillering nodes in Dn1 under low temperature stress.The KEGG analysis of its target genes showed that the key genes of JA signal transduction pathways—COI1 and MYC2,changed significantly,indicating that JA may participate in low temperature stress response.In this study,Dn1 was used as the experimental material.Trifoliate wheat leaves were treated with 0.5 mmol/L MeJA,1 mmol/L MeJA,2 mmol/L MeJA,and distilled water as a control.To investigate the effects of exogenous MeJA on physiology and determine the optimal concentration of JA when the natural temperature at 5°C,0°C,-10°C,and-25°C,the samples(leaves and tiller nodes)were taken.At this concentration,the effects of exogenous MeJA on JA response genes and key signal transduction pathways in JA signal transduction pathways were studied to reveal the molecular mechanism of COI1 and MYC2 response to low temperature stress in winter wheat,providing the theoretical and production basis.The results are as follow:(1)The effect of exogenous MeJA treatment on lipid peroxidation under low temperature stress: with the decrease of temperature,the relative conductivities and the content of malondialdehyde showed a gradually increasing trend in leaves and tillering nodes of the control and treatment groups,And the maximum expression level appears at-25°C;From the different organs,the relative electrical conductivity and the content of m alondialdehyde in tilling nodes were less than leaves.Exogenous MeJA treatment reduced the relative electrical conductivity and MDA content of leaf and tiller nodes under low temperature stress,and protected the stability of the tillering membrane system of winter wheat,which improved the cold resistance of winter wheat.(2)Effect of exogenous MeJA treatment on osmotic adjustment substances under low temperature stress: with the decrease of temperature,The proline content,soluble protein content and soluble sugar content in tilling nodes and leaves of the control and treatment components both increased first and then decreased,And the maximum expression level appears at-25°C;From the different organs,the proline content,soluble protein content and soluble sugar content of the treated and control groups all showed that tillering nodes were more than leaves.Exogenous MeJA treatment enhanced the accumulation of osmoregulatory substances,such as soluble protein,proline,and soluble sugar content in leaves and tillering nodes under low temperature stress,improved the water retention capacity and osmotic adjustment ability of tillering nodes,and improved cold resistance of winter wheat..(3)The effects of exogenous MeJA treatment on the activities of main antioxidative enzymes under low temperature stress: with the decrease of temperature,the SOD activities of the control and treatmentgroups were gradually increased and reached the peak at-25 °C.The activity of POD increased first and then decreased,And the maximum expression level appears at-10°C.CAT activity gradually decreased,and the maximum expression level appeared at 5°C.From the different organs,the SOD activities and CAT activity in tilling nodes were less than leaves.The activity of POD in tilling nodes were more than leaves Different concentrations of MeJA increased the activities of SOD,POD and CAT in leaves and tillering nodes of Dn1,and the 1 mmol/L MeJA treatment was more obvious.Exogenous MeJA treatment effectively increased the activities of antioxidant enzymes SOD,POD,and CAT in leaves and tillering nodes under low temperature stress,which eliminated a large number of reactive oxygen species,free radicals,and other toxic substances produced,and improved the antioxidant activity of plants and improve the cold resistance of winter wheat.(4)Compared with different treatment concentrations,the treatment with 1 mmol/L MeJA was the most significant.Under different low temperature stress,the accumulation of protective substances,protective enzyme activity and cold resistance were the most in leaves and tiller nodes at-10°C.The maximum overwinter survival rate of Dn1 is 91.5% under the treatment of 1 mmol/L MeJA.(5)With the decrease of temperature,the expression of Ta COI1,Ta MYC2,and Ta PDF1.2 genes in leaves and tillers of Dn1 increased under the treatment of 1 mmol/L exogenous MeJA.Its showed that the trend of first increase and then decrease,and the maximum expression level appeared at-10°C.The expression levels of Ta PDF1.2,Ta COI1,and Ta MYC2 in winter wheat leaves and tillers were significantly increased in exogenous MeJA treatments(P<0.05).Ta PDF1.2 is a JAresponsive gene,so the increase of gene expression indicates JA accumulation.Ta COI1 and Ta MYC2 are key genes in the JA signal transduction pathway.The increased expression level of Ta COI1 and Ta MYC2 initiates the transcription of downstream cold-related genes and enhances the cold resistance of plants.In summary,Exogenous MeJA treatment Improves the cold-resistance physiological response of Dn1 under low temperature stress,increases the expression of Ta PDF1.2,and increased the accumulation of endogenous JA in winter wheat,increased the relative expression of Ta COI1,Ta MYC2 and JA-responsive gene Ta PDF1.2 in the JA signal transduction pathway of Dn1,which increased the cold resistance of Dn1.