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One of the most destructive diseases, Gibberella stalk rot (GSR), caused by Fusarium graminearum, reduces maize yields significantly. An induced resistance response is a potent and cost-effective plant defense against pathogen attack. The functional counterpart of JAs, coronatine (COR), has attracted a lot of interest recently due to its ability to control plant growth and stimulate secondary metabolism. Although several studies have focused on COR as a plant immune elicitor to improve plant resistance to pathogens, the effectiveness and underlying mechanisms of the suppressive ability against COR to F. graminearum in maize have been limited. We investigated the potential physiological and molecular mechanisms of COR in modulating maize resistance to F. graminearum. COR treatment strongly enhanced disease resistance and promoted stomatal closure with H2O2 accumulation, and 10 μg/mL was confirmed as the best concentration. COR treatment increased defense-related enzyme activity and decreased the malondialdehyde content with enhanced antioxidant enzyme activity. To identify candidate resistance genes and gain insight into the molecular mechanism of GSR resistance associated with COR, we integrated transcriptomic and metabolomic data to systemically explore the defense mechanisms of COR, and multiple hub genes were pinpointed using weighted gene correlation network analysis (WGCNA). We discovered 6 significant modules containing 10 candidate genes: WRKY transcription factor (LOC100279570), calcium-binding protein (LOC100382070), NBR1-like protein (LOC100275089), amino acid permease (LOC100382244), glutathione S-transferase (LOC541830), HXXXD-type acyl-transferase (LOC100191608), prolin-rich extensin-like receptor protein kinase (LOC100501564), AP2-like ethylene-responsive transcription factor (LOC100384380), basic leucine zipper (LOC100275351), and glycosyltransferase (LOC606486), which are highly correlated with the jasmonic acid–ethylene signaling pathway and antioxidants. In addition, a core set of metabolites, including alpha-linolenic acid metabolism and flavonoids biosynthesis linked to the hub genes, were identified. Taken together, our research revealed differentially expressed key genes and metabolites, as well as co-expression networks, associated with COR treatment of maize stems after F. graminearum infection. In addition, COR-treated maize had higher JA (JA-Ile and Me-JA) levels. We postulated that COR plays a positive role in maize resistance to F. graminearum by regulating antioxidant levels and the JA signaling pathway, and the flavonoid biosynthesis pathway is also involved in the resistance response against GSR. [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]

In recent years, Spodoptera frugiperda (S. frugiperda, Smith) has invaded China, seriously threatening maize production. To explore an effective method to curb the further expansion of the harm of the S. frugiperda, this experiment used maize seedlings of the Zhengdan 958 three-leaf stage (V3) of maize as the material to study the effect of coronatine (COR) on the ability of maize to resist insects (S. frugiperda) at the seedling stage. The results showed that when maize was sprayed with 0.05 μM COR, the newly incubated larvae of S. frugiperda had the least leaf feeding. It was found that 0.05 μM COR significantly increased the contents of abscisic acid (ABA) and jasmonate (JA) in maize leaves through the determination of hormone content. Moreover, transcriptome sequencing revealed that the expression of six genes (ZmBX1, ZmBX2, ZmBX3, ZmBX4, ZmBX5 and ZmBX6), which are associated with the synthesis of benzoxazinoid, were upregulated. Nine genes (ZmZIM3, ZmZIM4, ZmZIM10, ZmZIM13, ZmZIM18, ZmZIM23, ZmZIM27, ZmZIM28 and ZmZIM38) of JA-Zim Domain (JAZ) protein in the JA signal pathway, and seven genes (ZmPRH19, ZmPRH18, Zm00001d024732, Zm00001d034109, Zm00001d026269, Zm00001d028574 and Zm00001d013220) of ABA downstream response protein Group A Type 2C Protein Phosphatase (PP2C) were downregulated. These results demonstrated that COR could induce anti-insect factors and significantly improve insect resistance in seedling maize, which laid a theoretical foundation for further study of the mechanism of COR improving insect resistance in seedling maize, and provided data references for the use of COR as an environmentally friendly pest control method. [ABSTRACT FROM AUTHOR]

Ethylene (ET) is critical importance in the growth, development, and stress responses of plants. Plant hormonal stress responses have been extensively studied, however, the role of ET in plant growth, especially plant height (PH) remains unclear. Understanding the genetic control for PH in response to ET will provide insights into the regulation of maize development. To clarify the genetic basis of PH-related traits of maize in response to ET, we mapped QTLs for PH, ear height (EH), and internode length above the uppermost ear (ILAU) in two recombinant inbred line (RIL) populations of Zea mays after ET treatment and in an untreated control (CK) group. Sixty QTLs for the three traits were identified. Twenty-two QTLs were simultaneously detected under both ET treatment and untreated control, and five QTLs were detected at two geographic locations under ET treatment only. Individual QTL can be explained 3.87–17.71% of the phenotypic variance. One QTL (q2PH9-1, q1PH9, q1EH9/q1ILAU9-1, q2ILAU9, and q2EH9) for the measured traits (PH, EH, ILAU) was consistent across both populations. Two QTLs (q2PH2-5, q2ILAU2-2, q1PH2-2, and q1ILAU2-2; q1PH8-1, q1EH8-1, q2PH8-1) were identified for up to two traits in both locations and populations under both ET treatment and untreated control. These consistent and stable regions are important QTLs of potential hot spots for PH, ear height (EH), and internode length above the uppermost ear (ILAU) response to ET in maize; therefore, QTL fine-mapping and putative candidate genes validation should enable the cloning of PH, EH, and ILAU related genes to ET response. These results will be valuable for further fine-mapping and quantitative trait nucleotides (QTNs) determination, and elucidate the underlying molecular mechanisms of ET responses in 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), a structural and functional mimic of jasmonates, is involved in a wide array of effects on plant development and defense response. The present study aims to investigate the role of COR, in counteracting drought stress by modulating reactive oxygen species (ROS) homeostasis, water balance, and antioxidant regulation in detached maize plants. Our results showed that COR can markedly decrease the water loss rate, but the antioxidants diphenyleneiodonium chloride (DPI) and dimethylthiourea (DMTU) eliminate the effect of water loss induced by COR. Using the dye 2′,7′-dichlorofluorescein diacetate (H2DCF-DA) loaded in the maize epidermis guard cells, it is observed that COR could increase ROS production, and then antioxidants DPI and DMTU decreased ROS production induced by COR. In addition, the expression of ZmRBOHs genes, which were associated with ROS generation was increased by COR in levels and ZmRBOHC was highly expressed in the epidermis guard cells. Moreover, COR-treated plants increased H2O2 and O2−· accumulation, antioxidant enzyme activities in control plants, while COR relieved the ROS accumulation and antioxidant enzyme activities under PEG treatment. These results indicated that COR could improve maize performance under drought stress by modulating ROS homeostasis to maintain water loss rate and antioxidant enzyme activities. [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]

Plant Growth Regulators (PGRs) are functional compounds known for enhancing plant growth and development. However, their environmental impact is a concern due to poor water solubility and the need for substantial organic solvents. Recently, nano-delivery systems have emerged as a solution, offering a broad range of applications for small molecule compounds. This study introduces a nano-delivery system for Triacontanol (TA), utilizing a star polymer (SPc), aimed at promoting maize growth and improving physiological indicators. The system forms nearly spherical nanoparticles through TA's hydroxyl group and SPc's tertiary amine group. The TA/SPc nano-complex notably outperforms separate TA or SPc treatments in maize, increasing biomass, chlorophyll content, and nutrient absorption. It elevates chlorophyll content by 16.4%, 10.0%, and 6.2% over water, TA, and SPc treatments, respectively, and boosts potassium and nitrate ion uptake by up to 2 and 1.6 times compared to TA alone, leading to enhanced plant height and leaf growth. qRT-PCR analysis further demonstrated that the nano-complex enhanced cellular uptake through the endocytosis pathway by up-regulating endocytosis-related gene expression. The employment of TEM to observe vesicle formation during the internalization of maize leaves furnishes corroborative evidence for the participation of the endocytosis pathway in this process. This research confirms that SPc is an effective carrier for TA, significantly enhancing biological activity and reducing TA dosage requirements. [Display omitted] • The spontaneous assembly of SPc with TA results in a reduction in particle size. • Foliar application with 1 μM TA/SPc nano-complex improved maize growth. • TA/SPc enhanced maize's ability to absorb potassium and nitrogen elements. • TA/SPc complex enhanced cellular uptake through the endocytosis pathway in maize. [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]

Cuticular wax is the outermost thin hydrophobic layer covering the surface of aerial plant parts, which provides a primary waterproof barrier and protection against different environmental stresses. The aim of the present study was to investigate the role of ethephon, as an ethylene-releasing compound, in counteracting drought stress by modulating cuticular wax biosynthesis, water balance, and antioxidant regulation in maize seedlings. Our results showed that ethephon significantly increased the ethylene evolution rate, regulate the expression of cuticular wax synthesis regulatory gene ZmERE and the wax biosynthetic genes ZmGL1 , ZmGL15 , ZmFDH1 , and ZmFAE1 , and promote cuticular wax accumulation in maize seedlings under normal or drought stress conditions. Moreover, ethephon was shown to might markedly reduce water loss and chlorophyll leaching in leaves, and maintain higher relative water content and leaf water potential under drought stress. Ethephon significantly decreased malondialdehyde and hydrogen peroxide concentrations and electrolyte leakage, but increased the accumulation of proline and the activities of SOD, POD, and CAT. In addition, ethephon resulted in an increase in the ratio of root and shoot under drought stress. These results indicated that ethephon could improve maize performance under drought stress by modulating cuticular wax synthesis to maintain water status and membrane stability for plant growth. [ABSTRACT FROM AUTHOR]

• Ethephon repressed internode cell elongation but advanced growth process. • Ethephon increases secondary cell wall related genes expression to inhibit elongation. • Ethephon promotes ethylene evolution but decreased IAA and GAs level in the internode. • ERF, MYB and NAC are involved in cell wall and hormone related pathway regulation. Ethephon efficiently regulates plant growth to modulate the maize (Zea mays L.) stalk strength and yield potential, yet there is little information on how ethylene governs a specific cellular response for altering internode elongation. Here, the internode elongation kinetics, cell morphological and physiological properties and transcript expression patterns were investigated in the ethephon-treated elongating internode. Ethephon decreased the internode elongation rate, shortened the effective elongation duration, and advanced the growth process. Ethephon regulated the expression patterns of expansin and secondary cell wall-associated cellulose synthase genes to alter cell size. Moreover, ethephon increased the activities and transcripts level of phenylalanine ammonia-lyase and peroxidase, which contributed to lignin accumulation. Otherwise, ethephon-boosted ethylene evolution activated ethylene signal and increased ZmGA2ox3 and ZmGA2ox10 transcript levels while down-regulating ZmPIN1a , ZmPIN4 and ZmGA3ox1 transcript levels, which led to lower accumulation of gibberellins and auxin. In addition, transcriptome profiles confirmed previous results and identified several transcription factors that are involved in the ethephon-modulated transcriptional regulation of cell wall biosynthesis and modification and responses to ethylene, gibberellins and auxin. These results indicated that ethylene-modulated auxin and gibberellins signaling mediated the transcriptional operation of cell wall modification to regulate cell elongation in the ethephon-treated maize internode. [ABSTRACT FROM AUTHOR]