Functional analysis of a late embryogenesis abundant protein ZmNHL1 in maize under drought stress

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.

Analysis of the molecular mechanisms regulating how ZmEREB24 improves drought tolerance in maize (Zea mays) seedlings

Drought stress is one of the most limiting factors of maize productivity and can lead to a sharp reduction in the total biomass when it occurs at the seedling stage. Improving drought tolerance at the seedling stage is of great importance for maize breeding. The AP2/ERF transcription factor family plays a critical role in plant response to abiotic stresses. Here, we used a preliminary previously-generated ranscriptomic dataset to identify a highly drought-stress-responsive AP2 gene, i.e., ZmEREB24. Compared to the wild type, the overexpression of ZmEREB24 in maize significantly promotes drought tolerance of transgenic plants at the seedling stage. CRISPR/Cas9-based ZmEREB24-knockout mutants showed a drought-sensitive phenotype. RNA-seq analysis and EMSA assay revealed AATGG.CT and GTG.T.GCC motifs as the main binding sites of ZmEREB24 to the promoters of downstream target genes. DAP-seq identified four novel target genes involved in proline and sugar metabolism and hormone signal transduction of ZmEREB24. Our data indicate that ZmEREB24 plays important biological functions in regulating drought tolerance by binding to the promoters of drought stress genes and modulating their expression. The results further suggest a role of ZmEREB24 in regulating drought adaptation in maize, indicating its potential importance for employing molecular breeding in the development of high-yield drought-tolerant maize cultivars.

Drought stress in maize: stress perception to molecular response and strategies for its improvement

Given the future demand for food crops, increasing crop productivity in drought-prone rainfed areas has become essential. Drought-tolerant varieties are warranted to solve this problem in major crops, with drought tolerance as a high-priority trait for future research. Maize is one such crop affected by drought stress, which limits production, resulting in substantial economic losses. It became a more serious issue due to global climate change. The most drought sensitive among all stages of maize is the reproductive stages and the most important for overall maize production. The exact molecular basis of reproductive drought sensitivity remains unclear due to genes' complex regulation of drought stress. Understanding the molecular biology and signaling of the unexplored area of reproductive drought tolerance will provide an opportunity to develop climate-smart drought-tolerant next-generation maize cultivars. In recent decades, significant progress has been made in maize to understand the drought tolerance mechanism. However, improving maize drought tolerance through breeding is ineffective due to the complex nature and multigenic control of drought traits. With the help of advanced breeding techniques, molecular genetics, and a precision genome editing approach like CRISPR-Cas, candidate genes for drought-tolerant maize can be identified and targeted. This review summarizes the effects of drought stress on each growth stage of maize, potential genes, and transcription factors that determine drought tolerance. In addition, we discussed drought stress sensing, its molecular mechanisms, different approaches to developing drought-resistant maize varieties, and how molecular breeding and genome editing will help with the current unpredictable climate change.