Abstract: 【Objective】Drought is an important factor that affects the growth and development of maize seriously. Through the mining of genes related to drought resistance in maize, transgene function verification and transcriptome analysis, analyze the molecular regulation mechanism of key genes in response to drought stress provides the theoretical basis for drought resistance molecular breeding and genetic improvement. 【Method】In this study, the maize inbred line B104 (wild-type, WT) was used as the background to construct the ZmIBH1-1 overexpression (ZmIBH1-1-OE) transgenic line by Agrobacterium-mediated method. The transgenic plants and lines were identified via screening transgenic plants for glufosinate-ammonium resistance, PCR detection of marker gene and target gene and expression analysis of target gene by qRT-PCR. We using the ZmIBH1-1-OE and WT transgenic lines as materials. Through drought treatment (20% PEG6000), phenotype identification and drought tolerance physiological and biochemical index determination were carried out to verify the drought resistance function of ZmIBH1-1; RNA-Seq was used to identify differentially expressed genes (DEGs) under drought stress at the 4-leaf stage; Combined with DAP-seq (DNA affinity purification sequencing) analysis, it is preliminarily determined that ZmIBH1-1 protein directly regulates downstream target genes related to drought resistance, and IGV (Integrative Genomics Viewer) was used to analyze the position of the ZmIBH1-1 protein binding candidate target gene, and then the Dual-Luciferase assay was used to verify the regulatory relationship between ZmIBH1-1 protein and target genes. 【Result】12 transformation events were obtained by genetic transformation of maize. In the T₃ generation, there were 458 plants in which the marker gene Bar and the target gene ZmIBH1-1 were simultaneously detected. The results of qRT-PCR showed that the expression level of ZmIBH1-1 in ZmIBH1-1-OE lines was significantly higher than that of WT and the expression levels of transformation events 3 and 8 were the highest, which were self-crossed to obtain T₄ generation for subsequent experiments. Under drought stress, the survival rate, the relative water content, the chlorophyll content, soluble protein content and the physiological and biochemical indicators (superoxide dismutase, peroxidase, catalase activity) of ZmIBH1-1-OE were higher than those of WT significantly, which indicating that the overexpression of ZmIBH1-1 in maize confers higher drought tolerance. The RNA-Seq results showed that there were 1 214 DEGs between WT and ZmIBH1-1-OE lines. Gene Ontology (GO) analysis showed that DEGs were mainly involved in biological processes, cell components and molecular functions, such as photosynthesis, stress response, dehydration response, etc. in biological processes; KEGG enrichment analysis showed that DEGs were mainly involved in the signal transduction of plant hormones, the metabolism and other processes. Combining the significantly DEGs of RNA-Seq and the target genes of ZmIBH1-1 obtained from DAP-seq analysis, it is preliminary identified 11 candidate target genes related to drought resistance that may be directly regulated by ZmIBH1-1, including 2 calcium signal related genes, 3 cysteine metabolism related genes, 1 bHLH transcription factor, 1 stress response protein, 1 glutathione transferase, 1 redox process protein and 2 ethylene response factor; Integrative genomics viewer showed that ZmIBH1-1 protein could bind to the promoters of the target genes; Subsequent Dual-Luciferase assay further showed that ZmIBH1-1 protein can directly act on 11 candidate target genes, of which, ZmIBH1-1 directly binds to the promoters of ZmCa-M, ZmSYCO, ZmbHLH54, ZmGlu-r1, ZmCLPB3 and ZmP450-99A2 to promote their expression, and directly binds to the promoters of ZmAGD12, ZmCYS, ZmCYSB, ZmERF-107 and ZmEIN3 to repress their expression. In addition, transcription factors such as NAC, WRKY and MYB also differentially expressed between WT and ZmIBH1-1-OE under drought stress. 【Conclusion】The overexpression of ZmIBH1-1 can enhance the drought tolerance of maize; ZmIBH1-1 improves the drought tolerance of maize by directly regulating the expression of genes ZmERF-107 and ZmEIN3 in the ethylene signaling pathway; ZmIBH1-1 enhances the drought tolerance of maize by directly regulating the calcium signal-related genes ZmCa-M and ZmAGD12; ZmIBH1-1 may indirectly regulate NAC, WRKY, MYB and other transcription factors in response to drought stress.

Key words: maize; drought stress; ZmIBH1-1; RNA-Seq, transcription factor, gene expression