Maize ZmBES1/BZR1-4 recruits ZmTLP5 to regulate drought tolerance and seed development by regulating ZmPum6 and ZmMBP1

Abstract

BES1/BZR1, a kind of plant-specific transcription factor (TF), has been reported to regulate growth, development, and stress response. However, the maize BES1/BZR1 members are still largely unknown. In this study, we investigated the function and regulatory mechanism of maize ZmBES1/BZR1-4 in regulating drought response and seed development. The ZmBES1/BZR1-4 was localized in the nucleus depending on its bHLH domain and showed no self-transactivation activity. The transcription level of ZmBES1/BZR1-4 was induced by drought stress and was predominantly higher in seeds 25 days after pollination. Overexpression of ZmBES1/BZR1-4 reduced drought tolerance but produced bigger seeds with higher seed weight in transgenic Arabidopsis, rice, and maize. Inversely, the ZmBES1/BZR1-4 mutant Mu4-1 and Mu4-2 showed enhancement of drought tolerance and decreased seed size and weight. The ZmBES1/BZR1-4 could directly bind to E-box elements in the ZmMBP1 and ZmPum6 promoters to activate their transcription. Furthermore, the interaction between ZmBES1/BZR1-4 and ZmTLP5 enhanced the ZmMBP1 and ZmPum6 transcription. Moreover, ZmMBP1 and ZmPum6 positively regulated seed size and weight, but ZmPum6 negatively regulated drought tolerance. Therefore, our findings reveal that ZmBES1/BZR1-4 recruits ZmTLP5 to regulate drought tolerance and seed development by regulating ZmMBP1 and ZmPum6, which contributes to uncovering the function of BES1/BZR1s regulating growth, development, and stress response in crops.