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Abstract MYB-related genes, a subclass of MYB transcription factor family, have been documented to play important roles in biological processes such as secondary metabolism and stress responses that affect plant growth and development. However, the regulatory roles of MYB-related genes in drought stress response remain unclear in maize. In this study, we discovered that a 1R-MYB gene, ZmRL6, encodes a 96-amino acid protein and is highly drought-inducible. We also found that it is conserved in both barley (Hordeum vulgare L.) and Aegilops tauschii. Furthermore, we observed that overexpression of ZmRL6 can enhance drought tolerance while knock-out of ZmRL6 by CRISPR-Cas9 results in drought hypersensitivity. DAP-seq analyses additionally revealed the ZmRL6 target genes mainly contain ACCGTT, TTACCAAAC and AGCCCGAG motifs in their promoters. By combining RNA-seq and DAP-seq results together, we subsequently identified eight novel target genes of ZmRL6 that are involved in maize's hormone signal transduction, sugar metabolism, lignin synthesis, and redox signaling/oxidative stress. Collectively, our data provided insights into the roles of ZmRL6 in maize’s drought response.

Seasonal drought is a major limiting factor for wheat production in the North China Plain. The use of non-destructive screening tools based on vegetation indices associated with physiological and biochemical traits will help in the identification of drought-tolerant wheat genotypes to counter drought stress. The objectives of this study were to characterize the performance of 10 wheat genotypes with different genetic backgrounds in terms of physical and biochemical traits under two contrasting moisture regimes, and to evaluate the effectiveness of vegetation indices/spectral measurement techniques for assessing drought tolerance in wheat. Traits associated with drought stress were assessed in the 10 wheat genotypes, including plant biophysical parameters, drought tolerance parameters, as well as various vegetation indices. Significant variability was found wheat genotypes with different genetic backgrounds to water stress. The clustering results indicated that Luohan-19, Luohan-22, and Jinmai-47 were drought-tolerant genotypes characterized by high stress tolerance index (STI) values (0.548, 0.535 and 0.523, respectively), drought index (DI) values (0.517, 0.524 and 0.504, respectively), and drought tolerance coefficient (DC) values (1.065, 1.074 and 1.000, respectively). Based on principal component analysis and membership function, genotypes were classified as tolerant (Luohan-19, Luohan-22, and Jinmai-47), moderately tolerant (Luomai-26, Zhongmai-175, and Bainong-207) and sensitive (Yunong-516, Zhongmai-895, Annong-0711 and Huacheng-3366) to water stress, with comprehensive evaluation values (D) of >0.761, 0.422–0.761, and 0.717), and are therefore recommended as rapid indicators for the identification of tolerance genotypes in the field. These vegetation indices, particularly NDWI and CIred edge, exhibited similar performance to the drought tolerance indices and multivariate data analysis results in identifying drought-tolerant genotypes, and thus they can be used as alternative and inexpensive measures for identifying drought tolerance in wheat in the future.

Conventional farming practices not only constrained food security due to low yield but also threatened the ecosystem by causing groundwater decline and groundwater nitrate contamination. A two׹ear field experiment was conducted at the research station of North China University of Water Resources and Electric Power, Zhengzhou. The WHCNS model was used to simulate grain yield, water and nitrogen fertilizer use efficiencies (WUE and FNUEs) of spring maize under border irrigation method, drip irrigation, and rainfed conditions. In addition, a scenario analysis was also performed on different dry and rainy seasons to assess the long-term impact of rainfall variability on spring maize from 2000–2017. The result showed that the model precisely simulated soil water content, N concentration, crop biomass accumulation, and grain yield. The maximum and minimum range of relative root mean squire error (RRMSE) values were 0.5–36.0% for soil water content, 14.0–38.0% for soil nitrate concentrations, 19.0–24.0% for crop biomass and 1.0–2.0% for grain yield, respectively under three irrigation methods. Both the index of agreement (IA) and Pearson correlation coefficient (r) values were close 1. We found the lowest grain yield from the rainfed maize, whereas the drip irrigation method increased grain yield by 14% at 40% water saving than border irrigation method for the two years with the 11% lower evaporation and maintained transpiration rate. Moreover, the drip irrigated maize had a negligible amount of drainage and runoff, which subsequently improved WUE by 27% in the first growing season and 16% in the second rotation than border irrigation. The drip irrigated maize also showed 24% higher FNUE. The reason of lower WUE and FNUEs under the border irrigation method was increased drainage amounts and N leaching rates. Furthermore, scenario analysis indicated that the dry season could result in a 30.8% yield decline as compared to rainy season.

In this study, green tea waste (GTW) was used to synthesize the iron oxide (IO) nanoparticles (IO@GTW) to facilitate the adsorption of heavy metals from wastewaters. To satisfy structural integrity needs, the synthesized IO@GTW was incorporated into a polyvinyl alcohol (PVA)/alginate polymer network to obtain PVA/alginate/IO (PAI) hydrogels. Experimental techniques of transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR) were subsequently used to confirm the successful synthesis of IO nanoparticles. Scanning electron microscopy (SEM) established the porous microstructure of PAI hydrogels, while FT-IR analysis revealed the physical incorporation of IO@GTW in PAI hydrogels. The adsorption of Cu2+ and Cr6+ on PAI hydrogels was subsequently investigated. The present study was able to show that the removal ratio and adsorption capacity of the synthesized PAI hydrogels depended on the pH, initial concentration of metal ions in the solution, and contact time. The equilibrium isotherms of Cu2+ and Cr6+ adsorption were well-described using Langmuir and Freundlich isotherm models. The adsorption kinetics of Cu2+ can be modelled using the pseudo-second-order model, and the adsorption kinetics of Cr6+ can be modelled using both pseudo-first-order and intraparticle diffusion models. This study, therefore, demonstrates the functionality of integrating green tea waste in a polymeric composite to perform as an effective and green adsorbent for heavy metal removal, thus indicating the viability of its future application in wastewater treatment operations.

Analyzing the transcriptome of maize leaves under drought stress and rewatering conditions revealed that transcription factors were involved in this process, among which ZmbZIP33 of the ABSCISIC ACID-INSENSITIVE 5-like protein 5 family was induced to significantly up-regulated. The functional mechanism of ZmbZIP33 in Abscisic acd (ABA) signaling pathway and its response to drought stress and rewatering has not been studied yet. The present study found that ZmbZIP33 contains a DNA-binding and dimerization domain, has transcriptional activation activity, and is highly homologous to SbABI1,SitbZIP68 and OsABA1. The expression of ZmbZIP33 is strongly up-regulated by drought, high salt, high temperature, and ABA treatments. Overexpression of ZmbZIP33 remarkably increased chlorophyll content and root length after drought stress and rewatering, and, moreover, cause an accumulation of ABA content, thereby improving drought resistance and recovery ability in Arabidopsis. However, silencing the expression of ZmbZIP33 (BMV-ZmbZIP33) remarkably decreased chlorophyll content, ABA content, superoxide dismutase and peroxidase activities, and increased stomatal opening and water loss rate compared with BMV (control). It showed that silencing ZmbZIP33 lead to reduced drought resistance and recovery ability of maize. ABA sensitivity analysis found that 0.5 and 1 μmol/L treatments severely inhibited the root development of overexpression ZmbZIP33 transgenic Arabidopsis. However, the root growth of BMV was greatly inhibited for 1 and 5μmol/L ABA treatments, but not for BMV-ZmbZIP33. Subcellular localization, yeast two-hybrid and BIFC further confirmed that the core components of ABA signaling pathways ZmPYL10 and ZmPP2C7 interacted in nucleus, ZmPP2C7 and ZmSRK2E as well as ZmSRK2E and ZmbZIP33 interacted in the plasma membrane. We also found that expression levels of ZmPYL10 and ZmSRK2E in the BMV-ZmbZIP33 mutant were lower than those of BMV, while ZmPP2C7 was the opposite under drought stress and rewatering. However, expression of ZmPYL10 and ZmSRK2E in normal maize leaves were significantly up-regulated by 3–4 folds after drought and ABA treatments for 24 h, while ZmPP2C7 was down-regulated. The NCED and ZEP encoding key enzymes in ABA biosynthesis are up-regulated in overexpression ZmbZIP33 transgenic line under drought stress and rewatering conditions, but down-regulated in BMV-ZmbZIP33 mutants. Together, these findings demonstrate that ZmbZIP33 played roles in ABA biosynthesis and regulation of drought response and rewatering in Arabidopsis and maize thought an ABA-dependent signaling pathway.

Increasing planting density is an important ways to increase maize yield. A hot topic of conversation in the current research is how to improve crop light efficiency and yield potential by optimizing the cultivation mode under high density planting is a hot topic in current research. Thus, in this study, a field experiment was conducted to explore the effects of stereo-planting patterns on water and the utilization light resource and maize yields. Planting patterns included the conventional flat planting pattern (as the control, CK) and the stereo-planting in ridge and furrow (T). Each planting pattern had three planting densities, i.e., 60,000 plants ha−1 (D1), 75,000 plants ha−1 (D2) and 90,000 plants ha−1 (D3). The results showed that stereo-planting affected the physiological characteristics of plants by changing the spatial distribution of soil moisture. At the silking stage (R1), photosynthetic rate (Pn) of plants on the ridge was similar to CK, and transpiration rate (Tr) was significantly lower than that of CK. Pn of maize in the furrow was significantly higher than that of CK, and Tr was similar to CK. Stereoscopic planting had different effects on intraspecific competition intensity in maize population in different growing stages. In the six-leaf stage (V6), stereo-planting increased competition intensity of maize on the ridge, but lowered that of maize in the furrow by affecting the spatial distribution of soil moisture. During the R1 stage, stereo-planting increased the light transmittance rate within the canopy and eased the plant’s competition for light by reducing plant height and leaf area of maize under three density conditions. Stereo-planting had no effect on grain yield and dry matter accumulation of ridge-planted maize in the later growing stage, but it did increased the dry matter accumulation and grain yield of furrow-planted maize due to the improvement of the light environment and photosynthetic characteristics of the population. In two test years, stereo-planting increased 5.0–11.0% average yield of maize compared to CK under three density conditions. These results indicate that stereo-planting can reduce the plant’s competition for light and water resources and improve its physiological traits of plant by optimizing its spatial distribution of soil moisture and canopy structure, thus further increasing grain yield of maize under high-density planting conditions.

OSCAs are hyperosmolality-gated calcium-permeable channel proteins. In this study, two co-expression modules, which are strongly associated with maize proline content, were screened by weighted correlation network analysis, including three ZmOSCA family members. Phylogenetic and protein domain analyses revealed that 12 ZmOSCA members were classified into four classes, which all contained DUF221 domain. The promoter region contained multiple core elements responsive to abiotic stresses and hormones. Colinear analysis revealed that ZmOSCAs had diversified prior to maize divergence. Most ZmOSCAs responded positively to ABA, PEG, and NaCl treatments. ZmOSCA2.3 and ZmOSCA2.4 were up-regulated by more than 200-fold under the three stresses, and showed significant positive correlations with proline content. Yeast two-hybrid and bimolecular fluorescence complementation indicated that ZmOSCA2.3 and ZmOSCA2.4 proteins interacted with ZmEREB198. Over-expression of ZmOSCA2.4 in Arabidopsis remarkably improved drought resistance. Moreover, over-expression of ZmOSCA2.4 enhanced the expression of drought tolerance-associated genes and reduced the expression of senescence-associated genes. We also found that perhaps ZmOSCA2.4 was regulated by miR5054.The results provide a high-quality molecular resource for selecting resistant breeding, and lay a foundation for elucidating regulatory mechanism of ZmOSCA under abiotic stresses.

The basic leucine zipper (bZIP) family of transcription factors (TFs) regulate diverse phenomena during plant growth and development and are involved in stress responses and hormone signaling. However, only a few bZIPs have been functionally characterized. In this paper, 54 maize bZIP genes were screened from previously published drought and rewatering transcriptomes. These genes were divided into nine groups in a phylogenetic analysis, supported by motif and intron/exon analyses. The 54 genes were unevenly distributed on 10 chromosomes and contained 18 segmental duplications, suggesting that segmental duplication events have contributed to the expansion of the maize bZIP family. Spatio-temporal expression analyses showed that bZIP genes are widely expressed during maize development. We identified 10 core ZmbZIPs involved in protein transport, transcriptional regulation, and cellular metabolism by principal component analysis, gene co-expression network analysis, and Gene Ontology enrichment analysis. In addition, 15 potential stress-responsive ZmbZIPs were identified by expression analyses. Localization analyses showed that ZmbZIP17, -33, -42, and -45 are nuclear proteins. These results provide the basis for future functional genomic studies on bZIP TFs in maize and identify candidate genes with potential applications in breeding/genetic engineering for increased stress resistance. These data represent a high-quality molecular resource for selecting resistant breeding materials.