Cloning And The Molecular Mechanism Of Negative Regulatory Drought Tolerance Of TaMYB44-5A In Wheat

Drought is one of the important limiting factors for wheat production.After drought stress,the growth rate of wheat slows down and the accumulation of dry matter slows down,resulting in a reduction in grain yield of more than 25%.More and more studies have shown that R2-R3 MYB transcription factors are involved in plant drought stress response.However,there are few reports of R2-R3 MYB transcription factors in wheat research.This study cloned the R2-R3 MYB transcription factor TaMYB44 in wheat,explored the biological function of TaMYB44-5A in response to drought stress,and analyzed the molecular mechanism of TaMYB44-5A negatively regulating plant drought tolerance.The main findings are as follows:(1)Identification and isolation of three homologous genes TaMYB44-5A,TaMYB44-5B,and TaMYB44-5D(Traes CS5A02G159600,Traes CS5B02G157300,Traes CS5D02G164600)of wheat TaMYB44 were isolated and located in the nucleus,encoding 336,349,and 348 amino acids,respectively.There are two SANT domains at the N-terminal of the three homologous genes,and the EAR conserved domain at the C-terminal.Promoter analysis found that TaMYB44-5A,TaMYB44-5B,and TaMYB44-5D promoter sequences had abundant cis-acting elements related to drought response.(2)After drought and PEG6000 treatment,the expression levels of wheat TaMYB44-5A,TaMYB44-5B,and TaMYB44-5D genes increased to varying degrees,indicating that the three have similar functions in response to drought stress.Among them,TaMYB44-5A has the highest expression level in wheat roots,stems,leaves,ears,and other tissues,and this gene will be the main target of follow-up research.(3)Under drought stress,overexpression of TaMYB44-5A decreased the proline content of Arabidopsis,weakened the sensitivity of Arabidopsis to exogenous abscisic acid,and increased leaf stomatal opening.At the same time,compared with WT,the expression levels of At P5CS1,At RD22,and other genes related to drought and abscisic acid responses were significantly decreased in transgenic Arabidopsis,which was consistent with the physiological phenotype of transgenic Arabidopsis after drought treatment.These results indicated that overexpression of TaMYB44-5A attenuated abscisic acid signaling-mediated stomatal movement,thereby reducing plant drought tolerance.(4)Arabidopsis leaves overexpressing TaMYB44-5A had a higher water loss rate and lower leaf relative water content under drought conditions,indicating that the ability of transgenic Arabidopsis to regulate stomatal movement was weakened.Transcriptional regulation showed that TaMYB44-5A directly binds to the promoter of abscisic acidresponsive gene TaRD22-3A through the MBS element and represses its transcription,which leads to the increase of leaf stomatal opening under drought stress.The above results indicated that TaMYB44-5A attenuated the abscisic acid signal-mediated stomatal movement by inhibiting the transcription of the abscisic acid-responsive gene TaRD22-3A,and ultimately reduced the drought tolerance of plants.In summary,wheat R2-R3 MYB transcription factor TaMYB44-5A directly targets the promoter of the abscisic acid response gene TaRD22-3A through the MBS element and inhibits its transcription weakens the ability to respond to abscisic acid signaling,and maintains a high stomatal opening degree,reduce the relative water content of leaves and ultimately lead to the weakening of drought tolerance of transgenic Arabidopsis.