Xiaoqiang Zhao

Salt stress is a significant environmental factor that inhibits maize growth and development, severely affecting yield formation. Interestingly, nanomaterials, particularly ZnONPs, can enhance resistance to various stresses and support healthy crop growth. However, the effects of ZnONPs on maize under salt stress remain unclear. This study investigates the effect of foliar and seed exposure to zinc oxide nanoparticles (ZnONPs) on reducing NaCl-induced salt stress in two maize inbred lines (NKY298-1 and NKY211). Over a period of seven days, under 120 mM NaCl, we measured growth, reactive oxygen species (ROS), malondialdehyde (MDA), membrane stability index (MSI), water status (relative water content, RWC), photosynthetic pigments and parameters, selected photosynthetic enzymes, and antioxidant enzyme activities. Then, we propose four composite indices, including stress improvement index (SII), alleviation capacity index (ACI), comprehensive improvement effects (CIE), and comprehensive alleviation capacity (CAC), to rank the effectiveness of ZnONP doses. The findings suggested that 50–100 μM ZnONPs significantly mitigate salt damage, with optimal doses varying by genotype (50 μM for NKY211 and 100 μM for NKY298-1). Notably, the study’s originality lies in its side-by-side composite scoring across 26 traits in two maize genotypes’ seedlings. In conclusion, the findings will provide a new idea for research on the molecular mechanism by which exogenous ZnONPs application improves the salt tolerance of maize seedlings.

Yield components are the most important breeding objectives, directly determining maize high-yield breeding. It is well known that these traits are controlled by a large number of quantitative trait loci (QTL). Therefore, deeply understanding the genetic basis of yield components and identifying key regulatory candidate genes can lay the foundation for maize marker-assisted selection (MAS) breeding. In this study, our aim was to identify the key genomic regions that regulate maize yield component formation through bioinformatic methods. Herein, 554 original QTLs related to 11 yield components, including ear length (EL), hundred-kernel weight (HKW), ear weight (EW), cob weight (CW), ear diameter (ED), cob diameter (CD), kernel row number (KRN), kernel number per row (KNR), kernel length (KL), grain weight per plant (GW), and kernel width (KW) in maize, were collected from the MaizeGDB, national center for biotechnology information (NCBI), and China national knowledge infrastructure (CNKI) databases. The consensus map was then constructed with a total length of 7154.30 cM. Approximately 80.32% of original QTLs were successfully projected on the consensus map, and they were unevenly distributed on the 10 chromosomes (Chr.). Moreover, 44 meta-QTLs (MQTLs) were identified by the meta-analysis. Among them, 39 MQTLs controlled two or more yield components, except for the MQTL4 in Chr. 1, which was associated with HKW; MQTL11 in Chr. 2, which was responsible for EL; MQTL19 in Chr. 3, which was related to KRN; MQTL26 in Chr. 5, which was involved in HKW; and MQTL36 in Chr. 7, which regulated EL. These findings were consistent with the Pearson correlation results, indicating that these traits exhibited co-linked heredity phenomena. Meanwhile, 159 candidate genes were found in all of the above MQTLs intervals, of which, 29 genes encoded E3 ubiquitin protein ligase, which was related with kernel size and weight. Other genes were involved in multiple metabolic processes, including plant hormones signaling transduction, plant growth and development, sucrose–starch synthesis and metabolism, and reproductive growth. Overall, the results will provide reliable genetic resources for high-yield molecular breeding in maize.

The germination and elongation of maize in the early growth stage are closely related to the elongation of the mesocotyl, which is one of the first parts to sense external temperature, aside from the coleoptile. Low-temperature (LT, 10~15 °C) stress can significantly affect the survival and growth of maize seedlings. Additionally, brassinosteroids (BRs) have been used in recent years to help alleviate damage caused by LT in various plants. However, the interaction among LT, BRs, and sugar remains unclear. Therefore, we examined the relationships among the contents of glucose, sucrose, and starch, along with the changes in differentially expressed genes (DEGs) involved in starch and sucrose metabolism and glycolysis/gluconeogenesis pathways. Compared to CK (0 μM 24-epibrassinolide (EBR) application at 25 °C), the contents of glucose and sucrose increased by 0.26, 0.47, and 0.70 mg g⁻¹ FW and 0.80, 0.30, and 0.61 mg g⁻¹ FW, respectively, under the CKE (2.0 μM 24-epibrassinolide (EBR) application at 25 °C), LT (0 μM 24-epibrassinolide (EBR) application at 10 °C), and LTE (2.0 μM 24-epibrassinolide (EBR) application at 10 °C) treatments. However, starch contents decreased under LT and LTE treatments, by −20.54% and −0.20%, respectively, compared to CK. This suggests that sugar signaling and metabolism play key roles in regulating LT tolerance, and the application of EBR may alleviate LT damage by regulating sugar accumulation levels. Furthermore, 108 DEGs were identified in the starch and sucrose metabolism pathways, along with 23 in glycolysis, with 65 DEGs at the transcriptome level. The common Zm00001d042146 (hexokinase-3) in both pathways is usually down-regulated, and the degree of down-regulation when EBR is added is less than under LT alone. Additionally, key genes such as Zm00001d021598 (glucan endo-1,3-beta-glucosidase 3), Zm00001d034017 (uncharacterized LOC541703), and Zm00001d029091 (sucrose synthase 2) were differentially expressed under LT, with their expression levels decreasing further when EBR was added. In conclusion, our results provide a new direction into the molecular mechanisms by which exogenous EBR application enhances low-temperature tolerance in maize seedlings.

Plant height (PH) and ear height (EH) are closely related to dense planting characteristics and lodging resistance of maize (Zea mays L.). Increasing the planting density will lead to changes in the structural characteristics of maize plants, such as reduced stem length and stem strength, thereby influencing their yield and quality. Therefore, analyzing the genetic basis of PH and EH in maize can provide valuable information for cultivating ideal plant types with suitable PH and EH. This study aims to identify stable genomic regions and candidate genes associated with PH and EH in maize through Meta-QTL (MQTL) analysis. A total of 187 original QTLs were collected from 13 published articles on QTL localization related to maize PH and EH. A high-density consistency map with a total length of 6970.00 cM was constructed, and 152 original QTLs were successfully projected into the consistency map. The remaining 35 QTLs could not be projected onto the consistency map, which may be attributed to a lack of common markers between the original and consistency map or to the QTL exhibiting low phenotypic variance explained (PVE), resulting in large confidence intervals (CIs). Then, 29 MQTLs were identified on 10 chromosomes via meta-analysis. Among them, the three identified MQTLs, i.e., MQTL4-1, MQTL4-2, and MQTL6-1, were specifically controlled by maize EH. Further analysis achieved 188 candidate genes in all MQTL intervals, which were related to maize plant development and morphogenesis. Meanwhile, the gene ontology (GO) enrichment analysis revealed that these candidate genes were involved in 77 GO annotations. These findings thus will help us better understand the molecular genetic basis of maize PH and EH under various environments, and thereby achieve an increased yield with maize dense planting breeding.

Low-temperature (LT) stress seriously affects the distribution, seedling survival, and grain yield of maize. At the seedling emergence stage, maize’s coleoptile is one of the most sensitive organs in sensing LT signaling and, in general, it can envelop young leaves to protect them from LT damage. In addition, brassinolides (BRs) have been shown to enhance LT tolerance from various species, but the effects of BRs on coleoptiles in maize seedlings under LT stress are unclear. Therefore, in this study, the pre-cultured coleoptiles of Zheng58 seedlings were treated with or without 2.0 μM 24-epibrassinolide (EBR) at 25 °C and 10 °C environments for five days to analyze their physiological and transcriptomic changes. Physiological analysis showed that a 10°C LT stress increased the content of glucose (0.43 mg g⁻¹ FW), sucrose (0.45 mg g⁻¹ FW), and starch (0.76 mg g⁻¹ FW) of Zheng58 coleoptiles compared to a 25°C environment. After the coleoptiles were exposed to a 2.0 μM EBR application under 10°C temperature for five days, the contents of these three sugars continued to increase, and reached 2.68 mg g⁻¹ FW, 4.64 mg g⁻¹ FW, and 9.27 mg g⁻¹ FW, respectively, indicating that sugar signaling and metabolism played key roles in regulating LT tolerance in the coleoptiles of maize seedlings. Meanwhile, a transcriptome analysis showed that 84 and 15 differentially expressed genes (DEGs) were enriched in the sucrose and starch metabolism and photosynthesis pathways, respectively, and multiple DEGs involved in these pathways were significantly up-regulated under LT stress and EBR stimulation. Further analysis speculated that the four DEGs responsible for sucrose-phosphate synthetase (SPS, i.e., Zm00001d048979, probable sucrose-phosphate synthase 5 and Zm00001d012036, sucrose-phosphate synthase 1), sucrose synthase (SUS, Zm00001d029091, sucrose synthase 2 and Zm00001d029087, sucrose synthase 4) were crucial nodes that could potentially link photosynthesis and other unknown pathways to form the complex interaction networks of maize LT tolerance. In conclusion, our findings provide new insights into the molecular mechanisms of exogenous EBR in enhancing LT tolerance of maize seedlings and identified potential candidate genes to be used for LT tolerance breeding in maize.

The plasticity elongation of mesocotyl (MES) and coleoptile (COL) largely determines the morphology of maize seedlings under abiotic stresses. The profilin (PRF) proteins play a pivotal role in cytoskeleton dynamics and plant development via regulating actin polymerization. However, little is known about whether and how the expression of the ZmPRF gene family regulates MES and COL elongation in maize under adverse abiotic stresses. Here, a total of eight ZmPRF gene members were identified in the maize genome. They were mainly located in the cytoplasm, chloroplast, and mitochondrion, and clearly divided into four classes, based on phylogenetic analysis. Segmental duplication was the main driver for the expansion of ZmPRF genes. Ka/Ks analysis indicated that most ZmPRF genes were intensely purified and selected. Promoter cis-element analysis suggested their potential roles in response to growth and development, stress adaption, hormone response, and light response. The protein–protein interaction network and two independent RNA-sequencing analyses revealed that eight ZmPRF genes and their thirty-seven interacting genes showed varied expression patterns in MES and COL of three maize genotypes under different sowing depths, 24-epibrassinolide application, and light spectral-quality treatments, of which ZmPRF3.3 was a potential core conserved gene for breeding application. Moreover, the quantitative real-time PCR (qRT-PCR) verified that the relative expression levels of most ZmPRF genes in MES and COL under above treatments were significantly correlated with the plasticity elongation of MES and COL in maize. Therefore, these results perform a comprehensive overview of the ZmPRF family and will provide valuable information for the validation of the function of ZmPRF genes in maize development under diverse abiotic stress.

Salt stress can seriously affect the growth and development of maize (Zea mays L.), resulting in a great yield loss. Melatonin (MT), an indole hormone, is a potential enhancer of plant tolerance against salt stress. However, the complex mechanisms of MT application in enhancing maize salt tolerance are still unclear. Herein, three-leaf seedlings of salt-susceptible P138 and its salt-resistant ethyl methane sulfonate (EMS)-104 mutant were cultured with or without 150 μM MT application under 0 and 100 mM Na₂CO₃ treatments for seven days, to systematically explore the response mechanisms of exogenous MT in improving the salt tolerance of maize. The results showed that salt stress triggered an escalation in reactive oxygen species production, enhanced multiple antioxidant enzymes’ activities, impaired cellular membrane permeability, inhibited photosynthetic pigment accumulation, and ultimately undermined the vigor and photosynthetic prowess of the seedlings. While suitable MT application counteracted the detrimental impacts of Na₂CO₃ on seedlings’ growth and photosynthetic capacity, the seedling length and net photosynthetic rate of P138 and EMS-104 were increased by 5.5% and 18.7%, and 12.7% and 54.5%, respectively. Quantitative real-time PCR (qRT-PCR) analysis further showed that MT application activated the expression levels of antioxidant enzyme-related genes (Zm00001d025106, Zm00001d031908, Zm00001d027511, and Zm00001d040364) and pigment biosynthesis-related genes (Zm00001d011819 and Zm00001d017766) in both maize seedlings under Na₂CO₃ stress; they then formed a complex interaction network of gene expression, multiple physiological metabolisms, and phenotype changes to influence the salt tolerance of maize seedlings under MT or Na₂CO₃ stress. To sum up, these observations underscore that 150 μM MT can alleviate salt injury of maize seedlings, which may provide new insights for further investigating MT regulation mechanisms to enhance maize seedlings’ salt resistance.

Plant stomata play a crucial role in photosynthesis by regulating transpiration and gas exchange. Meanwhile, environmental cues can also affect the formation of stomata. Stomatal formation, therefore, is optimized for the survival and growth of the plant despite variable environmental conditions. To adapt to environmental conditions, plants open and close stomatal pores and even regulate the number of stomata that develop on the epidermis. There are great differences in the leaf structure and developmental origin of the cell in the leaf between Arabidopsis and grass plants. These differences affect the fine regulation of stomatal formation due to different plant species. In this paper, a comprehensive overview of stomatal formation and the molecular networks and genetic mechanisms regulating the polar division and cell fate of stomatal progenitor cells in dicotyledonous plants such as Arabidopsis and Poaceae plants such as Oryza sativa and Zea mays is provided. The processes of stomatal formation mediated by plant hormones and environmental factors are summarized, and a model of stomatal formation in plants based on the regulation of multiple signaling pathways is outlined. These results contribute to a better understanding of the mechanisms of stomatal formation and epidermal morphogenesis in plants and provide a valuable theoretical basis and gene resources for improving crop resilience and yield traits.