Drought (D) and heat (H) are the two major abiotic stresses hindering cereal crop growth and productivity, either singly or in combination (D/+H), by imposing various negative impacts on plant physiological and biochemical processes. Consequently, this decreases overall cereal crop production and impacts global food availability and human nutrition. To achieve global food and nutrition security vis-a-vis global climate change, deployment of new strategies for enhancing crop D/+H stress tolerance and higher nutritive value in cereals is imperative. This depends on first gaining a mechanistic understanding of the mechanisms underlying D/+H stress response. Meanwhile, functional genomics has revealed several stress-related genes that have been successfully used in target-gene approach to generate stress-tolerant cultivars and sustain crop productivity over the past decades. However, the fast-changing climate, coupled with the complexity and multigenic nature of D/+H tolerance suggest that single-gene/trait targeting may not suffice in improving such traits. Hence, in this review-cum-perspective, we advance that targeted multiple-gene or metabolic pathway manipulation could represent the most effective approach for improving D/+H stress tolerance. First, we highlight the impact of D/+H stress on cereal crops, and the elaborate plant physiological and molecular responses. We then discuss how key primary metabolism- and secondary metabolism-related metabolic pathways, including carbon metabolism, starch metabolism, phenylpropanoid biosynthesis, γ-aminobutyric acid (GABA) biosynthesis, and phytohormone biosynthesis and signaling can be modified using modern molecular biotechnology approaches such as CRISPR-Cas9 system and synthetic biology (Synbio) to enhance D/+H tolerance in cereal crops. Understandably, several bottlenecks hinder metabolic pathway modification, including those related to feedback regulation, gene functional annotation, complex crosstalk between pathways, and metabolomics data and spatiotemporal gene expressions analyses. Nonetheless, recent advances in molecular biotechnology, genome-editing, single-cell metabolomics, and data annotation and analysis approaches, when integrated, offer unprecedented opportunities for pathway engineering for enhancing crop D/+H stress tolerance and improved yield. Especially, Synbio-based strategies will accelerate the development of climate resilient and nutrient-dense cereals, critical for achieving global food security and combating malnutrition.

The composition of soil dissolved organic matter (DOM) can reflect the soil maturity and fertilizer supply capacity. Fertilization is an important management strategy to regulate soil DOM transformation by regulating fertility, crop growth, microbial biomass and enzyme activity. However, there are few studies on the effect mechanism of fertilization to soil microecology. Here, the data from a fouryear fertilization experiment in Liaohe irrigation area of China was used to evaluate and quantify the biological and nutrient effect mechanism of fertilization on the three-dimensional fluorescence characteristics of DOM components by the three-dimensional fluorescence spectral area volume integral analysis method (EEM-FRI). The results showed that the combined application of organic and inorganic fertilizers had increased the proportion of soil humic acids and could affect the DOM contents in the soil depth. The single application of organic fertilizer had reduced the proportion of fulvic acids. The proportion of protein-like components was increased with the application of phosphate fertilizer. The single application of nitrogen fertilizer increased the proportion of microbial metabolites. The proportion of humic acids was decreased and the proportion of small molecule DOM was increased in the soil of planting spring maize and applying fertilizer. The planting of spring maize could increase the exogenous input and the terrigenous characteristics of soil DOM. The organic fertilizer could increase soil microbial source DOM. Fertilization measures had affected microbial biomass, enzyme activity and spring maize yield, regulated the degradation of DOM and affected the characteristics of DOM components. The yield of spring maize was negatively correlated with humic acids components and positively correlated with fulvic acids components. The characteristics of DOM components were affected by their sources, degradation of soil enzymes and crop growth. Fertilization measures had affected soil DOM components by supplying DOC, affecting microbial enzyme activities and regulating the growth of spring maize. Fertilization had mainly affected DOM components in soil layer of 10-20 cm. Mixed fertilization had affected soil DOM in deep layer (20-40 cm). Combined application of organic and inorganic fertilizers had increased the proportion of soil DOM, application of inorganic fertilizer, especially nitrogen fertilizer alone significantly reduced of fulvic acids component in DOM, application of N, P, K was beneficial to increase the proportion of microbial metabolites in DOM. The proportion of fulvic acids components in soil DOM could be used to characterize soil fertility and microbial activity, and its proportion was a key factor to affect crop yield.

Drought stress, particularly at the tasseling stage, is the most devastating abiotic factor and major contributor to yield reduction in maize (Zea mays L.). Despite recent scientific advances in deciphering maize drought stress responses, the overall picture of key genes and proteins regulating maize tasseling drought tolerance remains less understood. In this study, we conducted comparative physiological, transcriptomic and proteomic analyses to monitor the changes in the leaf tissues of two contrasting maize hybrid cultivars exposed to drought stress at the tasseling stage. We identified 1701 differentially expressed genes (DEGs) in RNA-sequence runs and 424 differentially expressed proteins (DEPs) from an iTRAQ-based analysis. Mapman analysis revealed several regulatory processes influenced by drought conditions, including signal transduction, cell-wall remodeling, cellular redox homeostasis and hormone metabolism that were observed at both mRNA and protein levels. However, transcription factor regulation and secondary metabolism were specifically identified at the transcript level, whereas photosynthesis was uniquely identified to be affected by drought stress at the protein level. Meanwhile, a weak correlation between DEGs and DEPs was observed, indicating the drought response of maize at tasseling stage is largely regulated post-transcriptionally. Furthermore, comparative physiological analysis and qRT-PCR results substantiated the trancriptomic and proteomic findings. Additionally, we screened ZmPOD, ZmRAV1, ZmTPP and performed phenotypical and physiological characterizations of transgenic Arabidopsis thaliana (Arabidopsis) lines and wild-type. Resultantly, the transgenic Arabidopsis lines exhibited stronger tolerance to drought than the WT. This functional verification reinforces the reliability of our omics-based candidate gene selection. Overall, our research provides insights on the drought-responsive genes and pathways mediating maize drought tolerance at the tasseling stage.

Introduction: Anthocyanins are important natural pigments and bioactive compounds in colored maize kernels. Although colored fresh-eating maize has attracted increasing attention because of its nutritional and functional value, the molecular basis underlying anthocyanin accumulation in maize kernels with different colors remains incompletely understood. Methods: In this study, four fresh-eating maize cultivars with contrasting kernel colors, including white (WN 2000), yellow (HN), multicolored (CN1), and black (HTN188), were used to investigate the mechanism of anthocyanin accumulation. Total anthocyanin content was measured across developmental stages, and integrated metabolomic and transcriptomic analyses were performed to identify anthocyanin-related metabolites, differentially expressed genes, and candidate regulatory factors associated with kernel pigmentation. Results: Metabolomic profiling identified 49 anthocyanin-related metabolites/features, with marked enrichment of cyanidin-, peonidin-, and pelargonidin-related compounds in the black maize cultivar HTN188. Transcriptomic analysis identified 12,557 differentially expressed genes among the four cultivars, which were mainly enriched in phenylpropanoid biosynthesis, flavonoid biosynthesis, glutathione metabolism, fructose and mannose metabolism, and glyoxylate and dicarboxylate metabolism pathways. Several anthocyanin biosynthetic genes and regulatory transcription factor candidates were upregulated in anthocyanin-rich kernels, including DFR (Zm00001d011438), MYB (Zm00001d003052), bHLH (Zm00001d015990), and NAC (Zm00001d012508). In particular, the expression of DFR (Zm00001d011438) was strongly positively correlated with total anthocyanin content. Weighted gene co-expression network analysis further identified gene modules and candidate hub regulators associated with anthocyanin accumulation. Discussion: These findings provide a comparative multi-omics perspective on anthocyanin accumulation in fresh-eating maize kernels of different colors. The results suggest that the high anthocyanin accumulation in black maize is associated with the coordinated enrichment of anthocyanin-related metabolites and the upregulation of key structural genes and transcription factors. This study provides candidate genes and regulatory information for future functional studies and anthocyanin-oriented breeding in fresh-eating maize.

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.