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Summary: Stomatal density (SD) is closely related to crop drought resistance. Understanding the genetic basis for natural variation in SD may facilitate efforts to improve water‐use efficiency. Here, we report a genome‐wide association study for SD in maize seedlings, which identified 18 genetic variants that could be resolved to seven candidate genes. A 3‐bp insertion variant (InDel1089) in the last exon of Zea mays (Zm) IRX15A (Irregular xylem 15A) had the most significant association with SD and modulated the translation of ZmIRX15A mRNA by affecting its secondary structure. Dysfunction of ZmIRX15A increased SD, leading to an increase in the transpiration rate and CO2 assimilation efficiency. ZmIRX15A encodes a xylan deposition enzyme and its disruption significantly decreased xylan abundance in secondary cell wall composition. Transcriptome analysis revealed a substantial alteration of the expression of genes involved in stomatal complex morphogenesis and drought response in the loss‐of‐function of ZmIRX15A mutant. Overall, our study provides important genetic insights into the natural variation of leaf SD in maize, and the identified loci or genes can serve as direct targets for enhancing drought resistance in molecular‐assisted maize breeding. [ABSTRACT FROM AUTHOR]

The lengths of the basal internodes is an important factor for lodging resistance of maize (Zea mays). In this study, foliar application of coronatine (COR) to 10 cultivars at the V8 growth stage had different suppression effects on the length of the eighth internode, with three being categorized as strong-inhibition cultivars (SC), five as moderate (MC), and two as weak (WC). RNA-sequencing of the eighth internode of the cultivars revealed a total of 7895 internode elongation-regulating genes, including 777 transcription factors (TFs). Genes related to the hormones cytokinin, gibberellin, auxin, and ethylene in the SC group were significantly down-regulated compared to WC, and more cell-cycle regulatory factors and cell wall-related genes showed significant changes, which severely inhibited internode elongation. In addition, we used EMSAs to explore the direct regulatory relationship between two important TFs, ZmABI7 and ZmMYB117, which regulate the cell cycle and cell wall modification by directly binding to the promoters of their target genes ZmCYC1 , ZmCYC3 , ZmCYC7 , and ZmCPP1. The transcriptome reported in this study will provide a useful resource for studying maize internode development, with potential use for targeted genetic control of internode length to improve the lodging resistance of maize. [ABSTRACT FROM AUTHOR]

Salt stress negatively affects maize growth and yield. Application of plant growth regulator is an effective way to improve crop salt tolerance, therefore reducing yield loss by salt stress. Here, we used a novel plant growth regulator B2, which is a functional analogue of ABA. With the aim to determine whether B2 alleviates salt stress on maize, we studied its function under hydroponic conditions. When the second leaf was fully developed, it was pretreated with 100 µM ABA, 0.01 µM B2, 0.1 µM B2, and 1 µM B2, independently. After 5 days treatment, NaCl was added into the nutrient solution for salt stress. Our results showed that B2 could enhance salt tolerance in maize, especially when the concentration was 1.0 µMol·L−1. Exogenous application of B2 significantly enhanced root growth, and the root/shoot ratio increased by 7.6% after 6 days treatment under salt stress. Compared with control, the ABA level also decreased by 31% after 6 days, which might have resulted in the root development. What is more, B2 maintained higher photosynthetic capacity in maize leaves under salt stress conditions and increased the activity of antioxidant enzymes and decreased the generation rate of reactive oxygen species by 16.48%. On the other hand, B2 can enhance its water absorption ability by increasing the expression of aquaporin genes ZmPIP1-1 and ZmPIP1-5. In conclusion, the novel plant growth regulator B2 can effectively improve the salt tolerance in maize. [ABSTRACT FROM AUTHOR]

Coronatine (COR) is a phytotoxin produced by the pathogen Pseudomonas syringae, it has a structure similar to that of jasmonates (JAs), but it is much more active as a plant growth regulator. The goal of this study was to gain more insight into the effect and the mechanism of COR effects on stalk characteristics are related lodging resistance of maize. The agronomic traits, stalk ultrastructure, and endogenous hormones in maize stalks were studied in field trails and greenhouses, using hybrid cultivar "Xianyu 335" (XY335), "Zhengdan 958" (ZD958) and inbred line B73 as materials in 2018 and 2019. Different concentration of COR were sprayed onto maize foliar surfaces at the seven-expanded-leaves (V7) stage. Foliar application with 10 µmol L−1 of COR at the V7 stage decreased plant and ear height, increased weight and diameter of the basal internodes, and increased penetration strength and stalk bending resistance. Compared to the control treatment, in COR-treated plants, salicylic acid (SA) and jasmonic acid (JA) were decreased significantly in stalks. The treatment of 10 µmol L−1 of COR enhanced lignin accumulation, the integrity, and the thickness of cell walls in maize stalks in the early stages of stem growth in the inbred line B73, as revealed by autofluorescence microscopy and scanning electron micrographs. Our results indicated that COR improved stalk bending resistance of maize not only by optimizing stalk morphological characteristics, but also by altering hormone levels, which may led to greater lignin accumulation, thickens cell wall, and decreased the area of vascular bundles. [ABSTRACT FROM AUTHOR]

Waterlogging negatively affects maize growth and yield. In this study, we found that ethylene played a vital role in plant adaptation to waterlogging. ET promotes better growth in seedlings under waterlogging conditions by altering root architecture and increasing lateral root formation by 42.1%. What's more, plants with high endogenous ethylene levels exhibited reduced sensitivity to waterlogging stress. ET also induced the formation of aerenchyma, a specialized tissue that facilitates gas exchange, in a different pattern compared to aerenchyma formed under waterlogging. Aerenchyma induced by ET was mainly located in the medial cortex of the roots and was not prone to decay. ethylene inhibited root elongation under normal conditions, but this inhibition was not alleviated under waterlogging stress. Upon activation of the ET signaling pathway, the transcription factor EREB90 promoted aerenchyma formation by enhancing the programmed cell death process. Overexpression of EREB90 resulted in increased waterlogging tolerance compared to wild type plants. Our findings suggest that pre-treatment of maize seedlings with ET before waterlogging stress can trigger the programmed cell death process and induce aerenchyma formation, thus improving waterlogging resistance. [ABSTRACT FROM AUTHOR]