ZmC2H2-149 negatively regulates drought tolerance by repressing ZmHSD1 in maize.

Drought is a major abiotic stress that limits maize production worldwide. Therefore, it is of great importance to improve drought tolerance in crop plants for sustainable agriculture. In this study, we examined the roles of Cys2 /His2 zinc-finger-proteins (C2H2-ZFPs) in maize's drought tolerance as C2H2-ZFPs have been implicated for plant stress tolerance. By subjecting 150 Ac/Ds mutant lines to drought stress, we successfully identified a Ds-insertion mutant, zmc2h2-149, which shows increased tolerance to drought stress. Overexpression of ZmC2H2-149 in maize led to a decrease in both drought tolerance and crop yield. DAP-Seq, RNA-Seq, Y1H and LUC assays additionally showed that ZmC2H2-149 directly suppresses the expression of a positive drought tolerance regulator, ZmHSD1 (hydroxysteroid dehydrogenase 1). Consistently, the zmhsd1 mutants exhibited decreased drought tolerance and grain yield under water deficit conditions compared to their respective wild-type plants. Our findings thus demonstrated that ZmC2H2-149 can regulate ZmHSD1 for drought stress tolerance in maize, offering valuable theoretical and genetic resources for maize breeding programmes that aim for improving drought tolerance.

ZmGI2 regulates flowering time through multiple flower development pathways in maize.

GIGANTEA (GI) encodes a component of the circadian clock core oscillator and has been identified as a regulatory pathway of the circadian rhythm and photoperiodic flowering in model plants. However, the regulatory pathway of GI affecting flowering time is unknown in maize. Here, we identified that the zmgi2 mutant flowered earlier than the wild type under long day (LD) conditions, whereas the difference in flowering time was not apparent under short day (SD) conditions. The 24 h optimal expression of the gene in the stem apex meristems (SAM) appeared at 9 h after dawn under LD conditions and at 11 h after dawn under SD conditions. DAP-Seq and RNA-Seq further revealed that ZmGI2 delays flowering by directly binding to the upstream regions of ZmVOZs, ZmZCN8 and ZmFPF1 to repress the expression of these genes and by directly binding to the upstream regions of ZmARR11, ZmDOF and ZmUBC11 to promote the expression of these genes. The genetic and biochemical evidence suggests a model for the potential role of ZmGI2 in regulating the flowering time-dependent photoperiodic pathway. This study provides novel insights into the function of ZmGIs in maize and further demonstrates their potential importance for floral transition. These results contribute to a comprehensive understanding of the molecular mechanisms and regulatory networks of GI transcription factors in regulating flowering time in maize.

A Nucleoporin NUP58 modulates responses to drought and salt stress in maize (Zea mays L.).

Nuclear pore complex (NUP) is the main transport channel between cytoplasm and nucleoplasm, which plays an important role in stress response. The function of NUPs was widely reported in yeast and vertebrate but rarely in plants. Here, we identified a nuclear pore complex (ZmNUP58), that is tightly associated with drought and salt tolerance phenotype accompanied with phenotypic and physiological changes under drought and salt stress. The overexpression of ZmNUP58 in maize (Zea mays L.) significantly promotes both chlorophyll content and activities of antioxidant enzymes under drought- and salt-stressed conditions. RNA-Seq analysis showed that ZmNUP58 could regulate the expression of genes related to phytohormone synthesis and signaling, osmotic adjustment substances, antioxidant enzyme system, cell wall biosynthesis, glucose metabolism and aquaporin. The results provide novel insights into the regulatory role of ZmNUP58 in improving drought and salt tolerance through regulating phytohormone and other stress response genes in maize.

ZmCCT regulates photoperiod-dependent flowering and response to stresses in maize.

BACKGROUND: Appropriate flowering time is very important to the success of modern agriculture. Maize (Zea mays L.) is a major cereal crop, originated in tropical areas, with photoperiod sensitivity. Which is an important obstacle to the utilization of tropical/subtropical germplasm resources in temperate regions. However, the study on the regulation mechanism of photoperiod sensitivity of maize is still in the early stage. Although it has been previously reported that ZmCCT is involved in the photoperiod response and delays maize flowering time under long-day conditions, the underlying mechanism remains unclear. RESULTS: Here, we showed that ZmCCT overexpression delays flowering time and confers maize drought tolerance under LD conditions. Implementing the Gal4-LexA/UAS system identified that ZmCCT has a transcriptional inhibitory activity, while the yeast system showed that ZmCCT has a transcriptional activation activity. DAP-Seq analysis and EMSA indicated that ZmCCT mainly binds to promoters containing the novel motifs CAAAAATC and AAATGGTC. DAP-Seq and RNA-Seq analysis showed that ZmCCT could directly repress the expression of ZmPRR5 and ZmCOL9, and promote the expression of ZmRVE6 to delay flowering under long-day conditions. Moreover, we also demonstrated that ZmCCT directly binds to the promoters of ZmHY5, ZmMPK3, ZmVOZ1 and ZmARR16 and promotes the expression of ZmHY5 and ZmMPK3, but represses ZmVOZ1 and ZmARR16 to enhance stress resistance. Additionally, ZmCCT regulates a set of genes associated with plant development. CONCLUSIONS: ZmCCT has dual functions in regulating maize flowering time and stress response under LD conditions. ZmCCT negatively regulates flowering time and enhances maize drought tolerance under LD conditions. ZmCCT represses most flowering time genes to delay flowering while promotes most stress response genes to enhance stress tolerance. Our data contribute to a comprehensive understanding of the regulatory mechanism of ZmCCT in controlling maize flowering time and stress response.