Drought Tolerance And Mechanism Of Transcription Factor ZmMYB39 In Maize

MYB transcription factors constitute one of the larger transcription factor families in plants,playing crucial roles in plant growth,development,defense regulation and stress responses.This study was to analyze the drought tolerance function and regulation mechanism of MYB transcription factor family member ZmMYB39 in maize.The protein characteristics of ZmMYB39 were analyzed by bioinformatics,and the expression pattern of ZmMYB39 gene in different tissues under drought stresses were analyzed by q RT-PCR.Finally,ZmMYB39 gene was transferred into maize recombinant inbred lines（RILs）B104to analyze the difference of drought tolerance between ZmMYB39 overexpressed lines and wild-type（WT）lines.The differential expressed genes（DEGs）between transgenic lines and WT lines were analyzed by RNA-sequencing（RNA-seq）.Our esearch shows:（1）Bioinformatics analysis of ZmMYB39 protein:the molecular weight of ZmMYB39 protein was 39.6 k Da,and the theoretical isoelectric point was 6.71.It was a hydrophilic protein,containing two MYB domains,without transmembrane structure.The secondary structure of ZmMYB39 protein was mainly composed ofα-helix and random coil,accounting for 44.90%and 41.32%,respectively.The phylogenetic tree analysis showed that ZmMYB39 was the most closely related to wheat Ta MYB33 protein.Transient expression test of maize protoplast indicated that ZmMYB39 protein was localized in nucleus.QRT-PCR analysis showed that the expression of ZmMYB39 in leaves was the highest,followed by coleoptile,and lowest in roots,and the expression of ZmMYB39 in leaves was significantly different from that in coleoptile and roots.The expression levels of ZmMYB39 in roots and coleoptile were significantly different under drought treatment compared with the control condition,which strongly suggested that ZmMYB39 might be involved in the response to drought in maize.（2）Analysis of drought tolerance function of ZmMYB39 transgenic maize:After two weeks of drought treatment,the plant height of transgenic seedlings was significantly higher than that of wild-type（WT）,and most transgenic plants gene recovered,while wild-type plants all died for rehydration 5 days later.Under drought stress,the survival rate of maize with ZmMYB39 gene was significantly higher than that of WT.Under normal conditions,there was no significant difference in physiological parameters between ZmMYB39 transgenic plants and WT seedlings.Under drought stress,the contents of H₂O₂ and MDA in ZmMYB39 transgenic plants were significantly lower than WT.（3）RNA-seq analysis of ZmMYB39 transgenic maize:the number of DEGs between BD（B104 Drought,Expression of wild type under drought condition）and MD（OE Drought,Expression of ZmMYB39 transgenic plants under drought condition）,BW（B104 Water,Expression of wild type under normal watering condition）and MW（OE Water,Expression of ZmMYB39 transgenic plants under normal watering condition）were determined.RNA-seq analysis showed that 135 and 80 DEGs were found between BD and MD,BW and MW,respectively.Under drought conditions,GO enrichment and KEGG pathway analysis of DEGs indicated that some genes involved in abscisic acid and salicylic acid biosynthesis,water stress response,calcium binding,hydrogen peroxide response and other processes,may be involved in the response of maize ZmMYB39 to drought signal.