ZmPIP1;6 confers drought tolerance in maize seedlings under the regulation of ZmIBH1-L1 and ZmPBL21

Drought stress is a major constraint on maize seedling establishment and yield stability. In this study, we functionally characterized ZmPIP1;6, that encodes a maize plasma membrane intrinsic protein, and investigated its regulation pathway and allelic variation in relation to drought tolerance. ZmPIP1;6 was predominantly expressed in seedling roots and was induced by drought stress. Functional analyses indicated that ZmPIP1;6 positively regulates drought tolerance in maize seedlings. We further showed that the transcription factor ZmIBH1-L1 directly binds to the ZmPIP1;6 promoter and activates its transcription. In addition, ZmPBL21 physically interacted with ZmPIP1; 6; moreover, transgenic rice expressing ZmPBL21 displayed enhanced tolerance to PEG-induced osmotic stress. Candidate gene association analysis identified a significant natural variation in ZmPIP1;6 associated with seedling drought tolerance, and a derived Cleaved Amplified Polymorphic Sequences marker was developed to target a key C/T polymorphism for marker-assisted selection. These findings demonstrate that ZmPIP1;6 is an important positive regulator of maize drought tolerance and provide both mechanistic insight and molecular tools for drought-resistance breeding.