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Climate change is predicted to be a major threat to crop yield due to increasing global temperatures and periods of unpredictable rainfall. Therefore, it is important to identify some new genes that can help plants cope with drought stress. In this study, a drought-induced homeodomain-leucine zipper (HD-Zip) I gene, ZmHDZ4, was isolated from maize and characterized for its role in drought stress. Transient expression experiments showed that ZmHDZ4 is localized to the nucleus. Yeast one-hybrid assays demonstrated that ZmHDZ4 has trans-activation activity, and that the minimal activation domain was ZmHDZ4-1. We found that overexpression of ZmHDZ4 in rice can enhance tolerance to drought and increase sensitivity to abscisic acid (ABA). Compared to wild-type plants, ZmHDZ4-expressing transgenic plants had lower relative electrolyte leakage (REL), lower malondialdehyde (MDA) levels, and increased proline contents under drought stress conditions, all of which may contribute to enhanced drought tolerance. Taken together, these results suggest that ZmHDZ4 functions as a transcriptional regulator that can positively affect plant drought tolerance. Thus, ZmHDZ4 is an excellent candidate gene with potential applications in molecular breeding to improve crop drought tolerance. [ABSTRACT FROM AUTHOR]

Abscisic acid (ABA)-, stress-, and ripening-induced (ASR) proteins are reported to be involved in drought stress responses. However, the function of maize ASR genes in enhancing drought tolerance is not known. Here, nine maize ASR members were cloned, and the molecular features of these genes were analyzed. Phenotype results of overexpression of maize ZmASR3 gene in Arabidopsis showed lower malondialdehyde (MDA) levels and higher relative water content (RWC) and proline content than the wild type under drought conditions, demonstrating that ZmASR3 can improve drought tolerance. Further experiments showed that ZmASR3-overexpressing transgenic lines displayed increased stomatal closure and reduced reactive oxygen species (ROS) accumulation by increasing the enzyme activities of superoxide dismutase (SOD) and catalase (CAT) under drought conditions. Moreover, overexpression of ZmASR3 in Arabidopsis increased ABA content and reduced sensitivity to exogenous ABA in both the germination and post-germination stages. In addition, the ROS-related, stress-responsive, and ABA-dependent pathway genes were activated in transgenic lines under drought stress. Taken together, these results suggest that ZmASR3 acts as a positive regulator of drought tolerance in plants. [ABSTRACT FROM AUTHOR]