Zmhdz9, an HD-Zip transcription factor, promotes drought stress resistance in maize by modulating ABA and lignin accumulation

Maize is the largest crop in the world in terms of both planting area and total yield, and it plays a crucial role in ensuring global food and feed security. However, in recent years, with climate deterioration, environmental changes, and the scarcity of freshwater resources, drought has become a serious limiting factor for maize yield and quality. Drought stress-induced signals undergo a series of transmission processes to regulate the expression of specific genes, thereby affecting the drought tolerance of plants at the tissue, cellular, physiological and biochemical levels. Therefore, in this study we investigated the HD-Zip transcription factor gene Zmhdz9, and yeast activation experiments demonstrated that Zmhdz9 exhibited transcriptional activation activity. Under drought stress, high abscisic acid (ABA) and lignin levels significantly improved drought resistance in maize. Yeast two-hybrid, bimolecular fluorescence complementation (BIFC) and pull-down experiments showed that Zmhdz9 interacted with ZmWRKY120 and ZmTCP9, respectively. Overexpression of Zmhdz9 and gene editing of ZmWRKY120 or ZmTCP9 improved maize drought resistance, indicating their importance in the drought stress response. Furthermore, Zmhdz9 promoted the direct transcription of ZmWRKY120 in the W-box, activating elements of the ZmNCED1 promoter, which encodes a key enzyme in ABA biosynthesis. Additionally, Zmhdz9 promoted direct transcription of ZmTCP9 in the GGTCA motif, activating elements of the ZmKNOX8 promoter, which encodes a key enzyme in lignin synthesis. This study showed that the regulation of ABA and lignin by Zmhdz9 is essential for drought stress resistance in maize.