Maize Improvement Research Articles

The C2H2‐type zinc finger transcription factor ZmDi19‐7 regulates plant height and organ size by promoting cell size in maize

SUMMARYThe drought‐induced protein 19 (Di19) gene family encodes a Cys2/His2 zinc‐finger protein implicated in responses to diverse plant stressors. To date, potential roles of these proteins as transcription factors remain largely elusive in maize. Here, we show that ZmDi19‐7 gene exerts pivotal functions in regulation of plant height and organ growth by modulating the cell size in maize. ZmDi19‐7 physically interacts with ubiquitin receptor protein ZmDAR1b, which is indispensable in ubiquitination of ZmDi19‐7 and affects its protein stability. Further genetic analysis demonstrated that ZmDAR1b act in a common pathway with ZmDi19‐7 to regulate cell size in maize. ZmDi19‐7, severing as a transcriptional factor, is significantly enriched in conserved DiBS element in the promoter region of ZmHSP22, ZmHSP18c, ZmSAUR25, ZmSAUR55, ZmSAUR7 and ZmXTH23 and orchestrates the expression of these genes involving in auxin‐mediated cell expansion and protein processing in the endoplasmic reticulum. Thus, our findings demonstrate that ZmDi19‐7 is an important newfound component of the ubiquitin‐proteasome pathway in regulation of plant height and organ size in maize. These discoveries highlight potential targets for the genetic improvement of maize in the future.

Appropriate water and nitrogen supply regulates the dynamics of nitrogen translocation and thereby enhancing the accumulation of nitrogen in maize grains

To improve nitrogen uptake and grain quality in maize, this study explores the dynamic processes of nitrogen accumulation, distribution, and translocation under varying water and nitrogen supplies, aiming to optimize water-nitrogen management practices. Field trials were conducted in Karamay, Xinjiang, in 2022 and 2023, with different irrigation levels (75 % ETc, 100 % ETc, 125 % ETc) and nitrogen application rates (0, 93, 186, 279 kg Nhm−2). The effects of water and nitrogen supply on nitrogen accumulation and distribution in aboveground maize organs were analyzed, and the dynamic characteristics of maize nitrogen accumulation were examined using the characteristic parameters of the Richards nitrogen accumulation equation. The results showed that beyond the W2N2 treatment (irrigation at 100 % ETc and nitrogen application of 186 kg N hm−2), increases in irrigation and nitrogen did not significantly enhance nitrogen accumulation per plant. Under W2N2, high levels of nitrogen were accumulated in maize leaf, stem, bract, cob, and grain. The nitrogen transfer among different organs and their contribution to grain nitrogen showed the following hierarchy: leaf > stem > cob > bract, with the contribution rates to grain nitrogen ranging from 26.16 % to 56.23 % over the two years. The Richards model accurately quantified the dynamic relationship between water-nitrogen supply and crop nitrogen accumulation, with the coefficient of determination (R²) ranging from 0.9864 to 0.9999 and the normalized root mean square error (NRMSE) from 0.70 % to 6.51 %. Optimal water-nitrogen supply significantly reduced the accumulated temperature required for maize to enter the rapid nitrogen accumulation phase and achieve maximum growth rates, while extending the duration of the rapid growth phase and increasing both the maximum growth rate and the average growth rate during this period. Grain nitrogen accumulation was positively correlated with nitrogen accumulation rates, as well as nitrogen accumulation and translocation in various organs. Under suitable irrigation and nitrogen application, the interactive effects of water and nitrogen (W × N) significantly increased both nitrogen accumulation and nitrogen accumulation rates, laying a foundation for nitrogen translocation to grains in the late growth stages and enhancing grain nitrogen accumulation. Thus, appropriate water and nitrogen supply can significantly influence nitrogen accumulation, distribution, and translocation processes in maize, regulating grain nitrogen accumulation. This study provides valuable information for nitrogen accumulation regulation and grain quality improvement in maize in Xinjiang and other regions with similar climatic conditions.

Nurturing the sustainable food systems: crafting policies and practices for crop diversification in Bangladesh

Bangladesh’s agriculture is highly rice-centric. Although economically rational, this is also risky, and arguably unsustainable. As a result, there is increasing interest in crop diversification (CD). This study examines the policy environment and the implementation of projects promoting CD in Bangladesh from 1971 to the present. An integrated analytical framework, developed by the International Wheat and Maize Improvement Center (CIMMYT) was used. Despite numerous policies and projects aimed at promoting CD, progress remains limited due to historical biases and various challenges. This research identifies a significant gap in existing approaches, which primarily focus on production aspects while neglecting market systems for new crops. Additionally, inadequate coordination among government agencies has impacted the effectiveness of projects implemented by development partners. The study highlights that CD efforts have been largely project-driven and short-lived, emphasizing the need for mainstreaming CD with dedicated annual funding to ensure long-term sustainability. Key challenges in funding, market development, and implementation are identified. The study recommends mainstreaming CD through annual budgets and enhancing market linkages. Furthermore, it provides actionable guidelines for policymakers and practitioners to effectively promote and sustain crop diversification in Bangladesh’s agriculture.

Conventional and Molecular Improvement of Maize for Drought Tolerance: Research Review

Maize (Zea mays L.) is an important staple crop for food, feed, and industry globally. Despite the importance of maize as a principal food crop in developing countries, drought is a major constraint that affects maize production, particularly in Sub-Saharan Africa, where maize is grown under rainfed conditions. Plant breeders have been striving to improve and develop drought-tolerant crops. Nevertheless, these efforts still cannot meet the demand for food security due to fast population growth and climatic change. Conventional maize breeding for drought tolerance follows a diverse approach that includes recurrent selection, backcrossing, pedigree breeding, and subsequently evaluating inbred lines and hybrids at optimum conditions, a managed screening site, and random stress across multiple environments. Molecular markers were used to select donor parents with drought-adaptive alleles and then integrated into elite maize lines to create a new population of drought-tolerant inbred lines.

Genetic improvement of drought stress tolerance in maize, recent advancements and future research direction

Maize is an imperative crop around the globe, and it provides several essential nutrients to humans and animals. Environmental changes seriously affect growth and productivity. Drought stress is one of the most important abiotic stresses, reducing maize growth and yield and threatening global food security. For decades, breeders have been trying to improve maize's ability to counter the toxic effects of drought stress. Drought tolerance is controlled by many genes and it complicates molecular breeding. The use of conventional breeding methods limited the development of drought tolerance in maize because of the complex nature of this trait. Hence, maize breeders have shifted their focus towards improvement of drought tolerance in maize at molecular level. Different molecular tools like quantitative trait loci (QTL) mapping, genome-wide-association-studies (GWAS), transcriptome analysis, transcription factor (TFs) analysis, and CRISPR/Cas9 have played a vital role in gene’s identification and their use in molecular breeding. These genomic regions have been proven very effective, and more studies are being conducted to increase their efficiency; however, the improvement level is limited because of the complex genetic mechanism of drought tolerance. Different review articles have been published on this aspect; however, a comprehensive and updated overview of drought tolerance needs to be included. The current review highlights the role of diverse molecular techniques to improve drought tolerance in maize. This review article will enhance the interest of researchers working on the genetic improvement of maize.

Genome-wide transcriptome and gene family analysis reveal candidate genes associated with potassium uptake of maize colonized by arbuscular mycorrhizal fungi

BackgroundPotassium (K) is an essential nutrient for plant growth and development. Maize (Zea mays) is a widely planted crops in the world and requires a huge amount of K fertilizer. Arbuscular mycorrhizal fungi (AMF) are closely related to the K uptake of maize. Genetic improvement of maize K utilization efficiency will require elucidating the molecular mechanisms of maize K uptake through the mycorrhizal pathway. Here, we employed transcriptome and gene family analysis to elucidate the mechanism influencing the K uptake and utilization efficiency of mycorrhizal maize.Methods and resultsThe transcriptomes of maize were studied with and without AMF inoculation and under different K conditions. AM symbiosis increased the K concentration and dry weight of maize plants. RNA sequencing revealed that genes associated with the activity of the apoplast and nutrient reservoir were significantly enriched in mycorrhizal roots under low-K conditions but not under high-K conditions. Weighted gene correlation network analysis revealed that three modules were strongly correlated with K content. Twenty-one hub genes enriched in pathways associated with glycerophospholipid metabolism, glycerolipid metabolism, starch and sucrose metabolism, and anthocyanin biosynthesis were further identified. In general, these hub genes were upregulated in AMF-colonized roots under low-K conditions. Additionally, the members of 14 gene families associated with K obtain were identified (ARF: 38, ILK: 4, RBOH: 12, RUPO: 20, MAPKK: 89, CBL: 14, CIPK: 44, CPK: 40, PIN: 10, MYB: 174, NPF: 79, KT: 19, HAK/HKT/KUP: 38, and CPA: 8) from maize. The transcript levels of these genes showed that 92 genes (ARF:6, CBL:5, CIPK:13, CPK:2, HAK/HKT/KUP:7, PIN:2, MYB:26, NPF:16, RBOH:1, MAPKK:12 and RUPO:2) were upregulated with AM symbiosis under low-K conditions.ConclusionsThis study indicated that AMF increase the resistance of maize to low-K stress by regulating K uptake at the gene transcription level. Our findings provide a genome-level resource for the functional assignment of genes regulated by K treatment and AM symbiosis in K uptake-related gene families in maize. This may contribute to elucidate the molecular mechanisms of maize response to low K stress with AMF inoculation, and provided a theoretical basis for AMF application in the crop field.

Investigating the Efficacy of Dry Region Zinc Solubilizing Bacteria for Growth Promotion of Maize and Wheat under Axenic Conditions

Zinc (Zn) plays a crucial role as a micronutrient, essential for the growth, development, and proper functioning of plants. Pakistani soils are deficient of micronutrient especially zinc. Supplementation of Zn fertilizers cannot do the job because only a small fraction of Zn is available to plants and rest is fixed in soil. To enhance the Zn availability different methods are being used which are expensive. Zinc solubilizing bacteria (ZSB) can be a potential candidate for solubilization of Zn and growth promoting activities in cereals. The present study aimed to evaluate the potential of dry region bacterial strains of Bahawalpur for improving Zn uptake and growth improvement in wheat and maize. Rhizosphere samples of wheat and maize were taken from the dry regions of Bahawalpur and bacterial strains were isolated and tested for their Zn solubilizing ability and screened for urease, siderophore activity, exopolysaccharide production, phosphorus solubilization and plant growth promoting abilities. Under axenic conditions selected isolates were further screened to assessed for improving the growth of wheat and maize seedlings. The rhizobacterial isolates IUB-34, IUB-80, IUB-93 and IUB-96 performed best to improve growth, physiology, biochemical attributes and root colonization. The maximum increase in root and shoot lengths were recorded 32.2 and 35.7% in wheat under IUB-34 application and in maize 43.8 and 39.9%, respectively, under IUB-96 application as compared to uninoculated control. Furthermore, maximum root colonization was also recorded under IUB-34 in wheat and IUB-96 in maize seedlings. Moreover, the biochemical characterization of selected isolates showed IAA (Auxins) production, protease, catalase, cellulose degradation, HCN and ACC-deaminase activities by these strains. However, only IUB-34 and IUB-96 were found positive for oxidase activity. Therefore, study concluded that use of dry region ZSB can solubilize Zn and make it available for plant to improve growth of wheat and maize. So, these isolates may be utilized for coating urea as a biofertilizer to increase the biofortification in cereals.

Comparative stress physiological analysis of aluminium stress tolerance of indigenous maize (Zea mays L.) cultivars of eastern Himalaya

Yield potential of maize having distinct genetic diversity in Eastern Himalayan Region (EHR) hill ecologies is often limited by Al toxicity caused due to soil acidity. Stress physiological analysis of local check exposed to 0–300 μM Al under sand culture revealed that 150 μM Al as critical and 200 μM Al as tolerable limit. Increase in Al from 0 to 300 μM reduced total chlorophyll, carotenoids by 74.8 % and 44.7 % respectively and enhanced anthocyanin by 35.3 % whereas LA, SLW and SL have reduced by 81.3%, 21.3 % and 47.8 % respectively. R/S ratio was 51.0 and 13.7 % higher at lower Al levels (50 μM and 100 μM) and photosynthetic, transpiration rate and TDM were 62.5 %, 42.9 % and 78.6 % lower at higher Al (300 μM) as compared to control. TRL, RSA, RDW and RV at higher Al (300 μM) were 92.6 %, 98.7 %, 78.7 and 97.5 % lower over control respectively. Root and shoot Al and PUpE at higher Al (300 μM) was 194.0, 69.2 and 830 % higher whereas PUE decreased to 88.5 % over control. Evaluation of 31 indigenous maize cultivars at 0, 150, and 250 μM Al in sand culture, alongside tolerance scoring and assessment, revealed that Megha-9, Megha-10, and MZM-19 exhibits high Al tolerance, Megha-1, MZM-22, and MZM-42 demonstrated moderate tolerance, whereas Uruapara, Sublgarh, and BRL Para were identified as Al-sensitive. Stress physiological parameters like SDW, TDM, TRL, SL and LA contributed 46.02 % of variability to PC1, whereas A, RV, RSA, anthocyanin and Chlorophyll_b, contributed 13.56 % of variability to PC2. Highest values of CMS, SL, LP, LA, TRL and anthocyanin were recorded in cluster I having sensitive cultivars while highest CMS, SL, LA, LP, TRL and RSA were found in cluster II having moderately tolerant cultivars and highest mean values for TRL, RSA, LP, LA, CMS and SL were recorded in cluster III having highly Al stress tolerant cultivars. The traits viz., A, RV, RSA, anthocyanin and Chlorophyll_b, total chlorophyll and TDM were emanated as physio-morphological for assessing Al toxicity stress tolerance in Maize with high divergence values. Tolerant cultivars showing 63.4 % and 22.4 % higher anthocyanin at 150 μM Al and 250 μM Al than moderately tolerant one in acid soil experiment with increased root Al, shoot Al, root P and shoot P by 42.6 %, 11 %, 95.1 % and 34 % respectively were emerged as promising for novel maize improvement under acid soils of EHR.

Weak-light stress at different grain filling stages affects yield by reducing leaf carbon and nitrogen metabolism in fresh waxy maize

Insufficient light radiation is one of the main factors limiting maize yield in southern China. The plum rainy season overlaps with grain filling stage, and intermittent cloudy and rainy weather results in weak-light stress restricting the yield improvement of fresh waxy maize. This study was to assess the impact of weak-light stress at different grain filling stages on yield and leaf carbon (C) and nitrogen (N) metabolism in fresh waxy maize. Suyunuo5 (SYN5) and Jingkenuo2000 (JKN2000) were used to investigate the effects of weak-light at different stages after pollination (1–7, 8–14, 15–21 and 1–21 days, recorded as Z1, Z2, Z3 and Z4) on yield, dry matter and nitrogen (N) accumulation, C and N metabolism in leaf of fresh waxy maize from 2021 to 2022. Compared with CK (natural light treatment), weak-light decreased the fresh ear and grain yield, post-silking dry matter and N accumulation, and the decrease was maximum in Z4, followed by Z1. The decrease in JKN2000 was greater than SYN5. RUBPCase and PEPCase activities, net photosynthetic rate, transpiration rate and stomatal conductance of ear leaves decreased under weak-light, and those were lowest in Z4, followed by Z1. Furthermore, weak-light stress significantly decreased the activities of nitrate reductase, glutamine synthetase, glutamate synthase, and post-silking N accumulation. The highest decrease was found in Z4, followed by Z1. Weak-light stress also downregulated the activities of superoxide dismutase, catalase, peroxidase and raised MDA content in ear leaves during grain filling stage, which accelerated leaf senescence process. Weak-light stress after pollination decreased maize yield by affecting leaf C and N metabolism and antioxidant system, and the stress occurred in first week after pollination had a more severe impact than those in middle and later stages, and JKN2000 was more sensitive to weak-light than SYN5. Our results contributed to understanding how weak-light stress could reduce the yield of fresh waxy maize by affecting leaf C and N metabolism, and offered theoretical support for implementing measures to alleviate weak-light conditions in the planting areas of fresh waxy maize.

Maize ZmLAZ1-3 gene negatively regulates drought tolerance in transgenic Arabidopsis

BackgroundMolecular mechanisms in response to drought stress are important for the genetic improvement of maize. In our previous study, nine ZmLAZ1 members were identified in the maize genome, but the function of ZmLAZ1 was largely unknown.ResultsThe ZmLAZ1-3 gene was cloned from B73, and its drought-tolerant function was elucidated by expression analysis in transgenic Arabidopsis. The expression of ZmLAZ1-3 was upregulated by drought stress in different maize inbred lines. The driving activity of the ZmLAZ1-3 promoter was induced by drought stress and related to the abiotic stress-responsive elements such as MYB, MBS, and MYC. The results of subcellular localization indicated that the ZmLAZ1-3 protein localized on the plasma membrane and chloroplast. The ectopic expression of the ZmLAZ1-3 gene in Arabidopsis significantly reduced germination ratio and root length, decreased biomass, and relative water content, but increased relative electrical conductivity and malondialdehyde content under drought stress. Moreover, transcriptomics analysis showed that the differentially expressed genes between the transgenic lines and wild-type were mainly associated with response to abiotic stress and biotic stimulus, and related to pathways of hormone signal transduction, phenylpropanoid biosynthesis, mitogen-activated protein kinase signaling, and plant-pathogen interaction.ConclusionThe study suggests that the ZmLAZ1-3 gene is a negative regulator in regulating drought tolerance and can be used to improve maize drought tolerance via its silencing or knockout.

Fine mapping and candidate gene analysis of qSRC3 controlling the silk color in maize (Zea mays L.).

Fine mapping of the maize QTL qSRC3, responsible for red silk, uncovered the candidate gene ZmMYB20, which encodes an R2R3-MYB transcription factor, has light-sensitive expression, and putatively regulates genes expression associated with anthocyanin biosynthesis. Colorless silk is a key characteristic contributing to the visual quality of fresh corn intended for market distribution. Nonetheless, the identification of Mendelian trait loci and associated genes that control silk color has been scarce. In this study, a F2 population arising from the hybridization of the single-segment substitution line qSRC3MT1 with red silk, carrying an introgressed allele from teosinte (Zea mays ssp. mexicana), and the recurrent maize inbred line Mo17, characterized by light green silk, was utilized for fine mapping. We found that the red silk trait is controlled by a semi-dominant genetic locus known as qSRC3, and its expression is susceptible to light-mediated inhibition. Moreover, qSRC3 explained 68.78% of the phenotypic variance and was delimited to a 133.2kb region, which includes three genes. Subsequent expression analyses revealed that ZmMYB20 (Zm00001d039700), which encodes an R2R3-MYB transcription factor, was the key candidate gene within qSRC3. Yeast one-hybrid and dual-luciferase reporter assays provided evidence that ZmMYB20 suppresses the expression of two crucial anthocyanin biosynthesis genes, namely ZmF3H and ZmUFGT, by directly binding to their respective promoter regions. Our findings underscore the significance of light-inhibited ZmMYB20 in orchestrating the spatial and temporal regulation of anthocyanin biosynthesis. These results advance the production of colorless silk in fresh corn, responding to the misconception that fresh corn with withered colored silk is not fresh and providing valuable genetic resources for the improvement of sweet and waxy maize.

Cytoplasmic genome contributions to domestication and improvement of modern maize

BackgroundStudies on maize evolution and domestication are largely limited to the nuclear genomes, and the contribution of cytoplasmic genomes to selection and domestication of modern maize remains elusive. Maize cytoplasmic genomes have been classified into fertile (NA and NB) and cytoplasmic-nuclear male-sterility (CMS-S, CMS-C, and CMS-T) groups, but their contributions to modern maize breeding have not been systematically investigated.ResultsHere we report co-selection and convergent evolution between nuclear and cytoplasmic genomes by analyzing whole genome sequencing data of 630 maize accessions modern maize and its relatives, including 24 fully assembled mitochondrial and chloroplast genomes. We show that the NB cytotype is associated with the expansion of modern maize to North America, gradually replaces the fertile NA cytotype probably through unequal division, and predominates in over 90% of modern elite inbred lines. The mode of cytoplasmic evolution is increased nucleotypic diversity among the genes involved in photosynthesis and energy metabolism, which are driven by selection and domestication. Furthermore, genome-wide association study reveals correlation of cytoplasmic nucleotypic variation with key agronomic and reproductive traits accompanied with the diversification of the nuclear genomes.ConclusionsOur results indicate convergent evolution between cytoplasmic and nuclear genomes during maize domestication and breeding. These new insights into the important roles of mitochondrial and chloroplast genomes in maize domestication and improvement should help select elite inbred lines to improve yield stability and crop resilience of maize hybrids.

Assessing the Potential of Extra-Early Maturing Multiple Stress-tolerant Maize Hybrids Under Different Rates of Nitrogen

Decline in soil fertility is a major constraint to maize production. This study aimed to assess the agronomic performance of improved maize varieties under different nitrogen rates to identify low nitrogen tolerant varieties. Five multiple stress-tolerant maize hybrids, developed by maize improvement program of the International Institute of Tropical Agriculture (IITA), and an open-pollinated variety used as check were evaluated under three levels nitrogen at two locations during 2019 growing season. The experiment was laid out in a split-plot experiment with three replications at each location. Nitrogen rates and varieties were the main and secondary factors, respectively. Data collected on grain yield and its related traits and were subjected to analysis of variance at 5% level of significance. The average grain yield of the six varieties under different nitrogen levels ranged from 2.2 t/ha at 0 kgN/ha in Angaradébou to 5.3 t/ha at 76 kgN/ha in Komkoma. Hybrid TZEEQI 342 × TZEEQI 7 showed high grain yield (4.0 t/ha) across the two agro-ecologies while varieties TZEE-W Pop STR QPM Co × TZEEQI 7 (3.7 t/ha) and TZdEEI 91 × TZEEI 21 (3.6 t/ha) had comparable grain yield. These hybrids were also less susceptible to nitrogen stress. They are the promising genotypes for Angaradébou localities while farmers around Komkoma should continue to cultivate TZEE-W Pop DT STR QPM.

Maize Improvement Based on Modern Breeding Strategies: Progress and Perspective

Maize Improvement Based on Modern Breeding Strategies: Progress and Perspective

Cytogenetics of maize in Mexico as a field of transnational exchange: The case of Takeo Ángel Kato Yamakake

Societal Impact StatementMaize is one of the most consumed grains worldwide. Its production and international trade are expected to continue increasing because of its use as animal fodder and direct human food. Although maize's history spans millennia, in the last century it underwent significant changes due to genetic engineering, particularly during the Green Revolution. Due to maize's importance for current food security and energy production, it is fundamental to understand this engineering process to assess the implications of current styles of maize production for local and global landscapes, scientific institutions, and transnational networks of agricultural science.Summary This article aims to explain how Mexican agricultural expertise contributed to the development of cytogenetics as a specialized field in the study of the diversity of maize within the framework of the Green Revolution. To this end, the article follows the work of Mexican agronomist Takeo Ángel Kato Yamakake within the activities of the Inter‐American Maize Improvement Program (IMIP), formally established in 1960. By reconstructing the debate on the genetic implications of chromosomal structure and function, this study contributes to the historiography devoted to the role played by local experts in the classification, experimentation, and conservation of maize. The article is based on sources from Mexico and the United States, an interview with Kato, and the consultation of the database “Rockefeller Fellows. Individual Mobility Awards at Rockefeller‐endowed Organizations, 1914‐1970.” Kato's trajectory provides an overview of agronomy in Mexico and shows the relevance of transnational exchange in the establishment of plant cytogenetics. Kato's academic activity features collaborations with key figures such as Edwin Wellhausen, Albert Longley, Barbara McClintock, W. Gallinat, Czeslawa Prywer, and Almiro Blumenschein. A Green Revolution era quest to unravel the origin of maize as a way of perfecting its genetic manipulation fueled the interest in establishing cytogenetics in Mexico. However, the irruption of the molecular approach made the study of the position of chromosomal knobs less of a priority. Despite this, classical cytogenetics, under Kato's leadership, remains a field that contributed to the knowledge of the vegetal genome, even when the IMIP disappeared and the logic of the Green Revolution lost its centrality.

Genetic dissection of resistance to gray leaf spot by genome-wide association study in a multi-parent maize population

BackgroundUnderstanding the genetic mechanisms underlying gray leaf spot (GLS) resistance in maize is crucial for breeding GLS-resistant inbred lines and commercial hybrids. Genome-wide association studies (GWAS) and gene functional annotation are valuable methods for identifying potential SNPs (single nucleotide polymorphism) and candidate genes associated with GLS resistance in maize.ResultsIn this study, a total of 757 lines from five recombinant inbred line (RIL) populations of maize at the F7 generation were used to construct an association mapping panel. SNPs obtained through genotyping-by-sequencing (GBS) were used to perform GWAS for GLS resistance using a linear mixture model in GEMMA. Candidate gene screening was performed by analyzing the 10 kb region upstream and downstream of the significantly associated SNPs linked to GLS resistance. Through GWAS analysis of multi-location phenotypic data, we identified ten candidate genes that were consistently detected in two locations or from one location along with best linear unbiased estimates (BLUE). One of these candidate genes, Zm00001d003257 that might impact GLS resistance by regulating gibberellin content, was further identified through haplotype-based association analysis, candidate gene expression analysis, and previous reports.ConclusionsThe discovery of the novel candidate gene provides valuable genomic resources for elucidating the genetic mechanisms underlying GLS resistance in maize. Additionally, these findings will contribute to the development of new genetic resources by utilizing molecular markers to facilitate the genetic improvement and breeding of maize for GLS resistance.

Genetic analysis of tolerance to combined drought and heat stress in tropical maize.

Simultaneous occurrences of heat and drought stresses have a detrimental effect on growth, development and yield of maize. Heat and drought is expected to worsen maize yield losses under climate change. Selecting CDHS tolerant maize hybrids creates great opportunity for sustainable maize improvement in the tropics. The objective of current investigation was to dissect the genetic basis of CDHS tolerance in tropical maize and to determine performance of single cross hybrids under CDHS. Ninety six single-cross hybrids resulted from crossing 12 tassel blast tolerant and 12 tassel blast susceptible lines along with two Striga resistant commercial hybrids, a heat tolerant and a heat susceptible check hybrids were evaluated under FIRR, MDRTS and CDHS using 25x4 alpha lattice design with two replications. The results showed significant genetic variation for FIRR, MDRTS and CDHS tolerance among maize hybrids. The majority of single crosses that showed improved grain yield over their respective standard checks under MDRTS also exhibited improved grain yield over the same checks under CHDS, indicating development of CHDS tolerance hybrids. Significant and positive genotypic and phenotypic correlation of grain yield under MDRTS and CDHS implicated common genetic mechanisms controlling yield under MDRTS and CDHS. Stress tolerance indices YI, GMP, MP, HM and STI were identified as best selecting indices under both stresses. GCA variances were larger than SCA variances in each testing environment for most studied traits indicating the impotence of additive gene action than non-additive gene action to control these traits. Majority of stress indices and SCA effects demonstrated that hybrids HB18, HB41, HB91 and HB95 were high yielder under MDRTS and CDHS. Hybrids HB41, HB91 and HB95 and their parents' scored minimum tassel blast. Parents 19 and 7 were well general combiner for grain yield and early maturity under MDRTS and CDHS indicting their valuable source of genes for hybridization. The current findings revealed that CDHS tolerance hybrids can reduce expected yield losses and maintain maize productivity in CDHS prone areas. Promising hybrids should be tested further under various drought and CHDS for commercialization.

DArTseq-based SNP markers reveal high genetic diversity among early generation fall armyworm tolerant maize inbred lines.

Diversity analysis using molecular markers serves as a powerful tool in unravelling the intricacies of inclusivity within various populations and is an initial step in the assessment of populations and the development of inbred lines for host plant resistance in maize. This study was conducted to assess the genetic diversity and population structure of 242 newly developed S3 inbred lines using 3,305 single nucleotide polymorphism (SNP) markers and to also assess the level of homozygosity achieved in each of the inbred lines. A total of 1,184 SNP markers were found highly informative, with a mean polymorphic information content (PIC) of 0.23. Gene diversity was high among the inbred lines, ranging from 0.04 to 0.50, with an average of 0.27. The residual heterozygosity of the 242 S3 inbred lines averaged 8.8%, indicating moderately low heterozygosity levels among the inbred lines. Eighty-four percent of the 58,322 pairwise kinship coefficients among the inbred lines were near zero (0.00-0.05), with only 0.3% of them above 0.50. These results revealed that many of the inbred lines were distantly related, but none were redundant, suggesting each inbred line had a unique genetic makeup with great potential to provide novel alleles for maize improvement. The admixture-based structure analysis, principal coordinate analysis, and neighbour-joining clustering were concordant in dividing the 242 inbred lines into three subgroups based on the pedigree and selection history of the inbred lines. These findings could guide the effective use of the newly developed inbred lines and their evaluation in quantitative genetics and molecular studies to identify candidate lines for breeding locally adapted fall armyworm tolerant varieties in Ghana and other countries in West and Central Africa.

ZmB12D, a target of transcription factor ZmWRKY70, enhances the tolerance of Arabidopsis to submergence

Submergence stress represents a serious threat to the yield and quality of maize because it can lead to oxygen deficiency and the accumulation of toxic metabolites. However, the mechanisms by which maize resists the adverse effects of submergence stress have yet to be fully elucidated. Here, we cloned a gene from maize Balem (Barley aleurone and embryo), ZmB12D, which was expressed at significant levels in seed embryos during imbibition and in leaves under submergence stress. Subcellular localization analysis indicated that the ZmB12D protein was localized in the mitochondria. The overexpression of ZmB12D in increased the tolerance of Arabidopsis to submergence stress, probably due to a reduction in the levels of malonaldehyde (MDA), the increased activity of antioxidant enzymes (SOD, POD and CAT), enhanced electron transport by coordinating the expression of non-symbiotic hemoglobin-2 (AHb2) and Fe transport-related (AtNAS3) genes (mediating Fe and oxygen availability) and also modulated the anaerobic respiration rates through upregulated the AtPDC1, AtADH1, AtSUS4 genes under submergence. Yeast one-hybrid (Y1H) and transient transactivation assays demonstrated that ZmWRKY70 bound to the ZmB12D promoter and activated ZmB12D. Collectively, out findings indicate that ZmB12D plays an important role in the tolerance of maize to submergence stress. This research provides new insights into the genetic improvement of maize with regards to submergence tolerance.

Gene editing of ZmGA20ox3 improves plant architecture and drought tolerance in maize.

Editing ZmGA20ox3 can achieve the effect similar to applying Cycocel, which can reduce maize plant height and enhance stress resistance. Drought stress, a major plant abiotic stress, is capable of suppressing crop yield performance severely. However, the trade-off between crop drought tolerance and yield performance turns out to be significantly challenging in drought-resistant crop breeding. Several phytohormones [e.g., gibberellin (GA)] have been reported to play a certain role in plant drought response, which also take on critical significance in plant growth and development. In this study, the loss-of-functionmutations of GA biosynthesis enzyme ZmGA20ox3 were produced using the CRISPR-Cas9 system in maize. As indicated by the result of 2-year field trials, the above-mentioned mutants displayed semi-dwarfingphenotype with the decrease of GA1, and almost no yield loss was generated compared with wild-type(WT)plants. Interestingly, as revealed by the transcriptome analysis, differential expressed genes (DEGs) were notably enriched in abiotic stress progresses, and biochemicaltests indicated the significantly increased ABA, JA, and DIMBOA levels in mutants, suggesting that ZmGA20ox3 may take on vital significance in stress response in maize. The in-depth analysis suggested that the loss function of ZmGA20ox3 can enhance drought tolerance in maize seedling, reduce Anthesis-Silking Interval (ASI)delay while decreasing the yield loss significantly in the field under drought conditions. The results of this study supported that regulating ZmGA20ox3 can improve plant height while enhancing drought resistance in maize, thus serving as a novel method for drought-resistant genetic improvement in maize.