The Mechanisms Of The Phenylpropanoid Pathway And MYB Transcription Factor TaMpc1-D4 In Responses To Drought Stress In Wheat

Wheat is the most important food crop in arid and semi-arid regions of northern China.Frequent drought will lead to the insufficient grain filling,which will seriously restrict the wheat production in China and even in the world.The flag leaf withers and senescences,but the spike has higher drought resistance and more durable photosynthetic characteristics,which is beneficial to the grain filling process under drought conditions.Phenylpropanoid pathway is a very important pathway in plants.It participates in plant resistance to stress and can also be used as an active oxygen scavenger.The MYB transcription factors family can regulate phenylpropanoid metabolism and participate in response to stresses such as drought.The mechanism of MYB transcription factors in response to drought stress was focused on the model plants,such as Arabidopsis thaliana and tobacco,and lacked the direct evidence in wheat.This study is based on the deficiencies of phenylpropane metabolism in wheat drought resistance research,and in view of the importance of the functional study of wheat MYB transcription factor family.Aiming at the characteristics of current photosynthetic persistence and delayed senescence of spike organs in dry land wheat.First,the differences of the enzyme activities and gene expression involved in the phenylpropanoid pathway in wheat spikes under drought conditions were mainly discussed.MYB transcription factors related to phenylpropanoid metabolism were identified in wheat by bioinformatics and other methods,and their gene expression patterns were analyzed under drought stress.Subsequently,the gene function of TaMpc1-D4 was used as the starting point,and the technical functions of VIGS silencing and genetic transformation were used to systematically analyze the TaMpc1-D4 gene function.The biological function of TaMpc1-D4 transcription factor and the expression differences between organs were investigated.It will reveal the regulatory mechanism of TaMpc1-D4 in the phenylpropanoid pathway,and clarify the molecular mechanism of its response to drought stress.?1?Compared with flag leaves,photosynthetic parameters,RWC and Chl contents were less affected by drought stress in wheat spike organs.The enzyme activities of PAL,C4H and4CL in flag leaf and spike organs of wheat were showed a trend of first increase and then decrease throughout the filling stage.Drought promoted the increase of these enzyme activities.The enzyme activity of wheat spike organs during the middle and late grain filling stages continued to increase and reached a peak.Under drought conditions,the contents of TPC and TFC were also increased.Under drought conditions,the phenylpropanoid pathway-related genes were induced during the middle and late grain filling periods.The antioxidant enzyme activity and proline were higher during the middle and late grain filling stages,which was beneficial to the removal of active oxygen and has a better osmotic adjustment effect.?2?Nine wheat MYB transcription factors involved in the phenylpropanoid pathway were screened.These transcription factors were all typical R2R3 type.Analysis of cis-acting elements indicated that they may be participated in the response to various hormonal and abiotic stresses.The phenylpropanoid pathway and the expression patterns of MYB transcription factors indicated that the insensitive to water of wheat spike organs may be closely related to the structural gene expression of the phenylpropanoid metabolism and the related MYB transcription factors that regulate the phenylpropanoid metabolism.?3?The TaMpc1-D4 gene was induced in the presence of exogenous PEG and ABA,and its localition was in the nucleus.TaMpc1-D4 had the transcription-activating activity at the C-terminus,but it lost the function when the full length was existed.?4?TaMpc1-D4 transgenic Arabidopsis plants had a higher water loss rate and were more sensitive to water.After mannitol treatment,the germination rate decreased and the root length became shorter.Ovexpression of TaMpc1-D4 transgenic Arabidopsis plants increased the O₂.^-and MDA contents,decreased the chlorophyll and proline?Pro?contents under drought treatment.The activities of peroxidase?POD?,superoxide dismutase?SOD?and catalase?CAT?were also decreased,and the expression of stress-related genes were significantly repressed.At the same time,the phenylpropanoid pathway was inhibited,and the contents of its metabolites TPC and TFC were also significantly decreased after drought treatment.The expression of structural genes related to the phenylpropanoid metabolism were also repressed to varying degrees.All the results showed that TaMpc1-D4 transgenic plants reduced the drought tolerance of transgenic Arabidopsis thaliana by weakening the activities of antioxidant enzyme,phenylpropane pathway,and inhibiting the expression of stress genes and phenylpropane metabolic related genes.?5?TaMpc1-D4 gene silencing plants had higher drought tolerance,higher RWC content,and better water holding capacity.In the TaMpc1-D4 gene silencing plants,the O₂.^-and MDA contents were decreased,and the Pro content was increased,and the enzyme activities of antioxidant enzymes?POD,SOD,and CAT?were increased,and the expression of drought-related stress-related genes was also induced after drought treatment.Menwhile,the phenylpropanoid pathway was strengthened,and the contents of its metabolites TPC and TFC were increased significantly after drought treatment.And the expression of structural genes related to phenylpropanoid metabolism were also induced.These results indicated that the TaMpc1-D4 gene silencing plants may enhance drought tolerance by strengthening the antioxidant enzymes,the phenylpropanoid pathway and inducing the expression of stress-related genes and genes related to the phenylpropanoid metabolism under drought stress.