Background: The WRKY transcription factor family plays significant roles in biotic and abiotic stress responses, which has been associated with various biological processes in higher plants. However, very little is known regarding the structure and function of WRKY genes in maize. Results: In this study, a total of 140 ZmWRKY proteins encoded by 125 ZmWRKY genes were eventually identified in maize. On the basis of features of molecular structure and a comparison of phylogenetic relationships of WRKY transcription factor families from Arabidopsis, rice and maize, all 140 ZmWRKY proteins in maize were divided into three main groups (Groups I, II and III) and the Group II was further classified into five subgroups. The characteristics of exon-intron structure of these putative ZmWRKY genes and conserved protein motifs of their encoded ZmWRKY proteins were also presented respectively, which was in accordance with the group classification results. Promoter analysis suggested that ZmWRKY genes shared many abiotic stress-related elements and hormone-related elements. Gene duplication analysis revealed that the segmental duplication and purifying selection might play a significant role during the evolution of the WRKY gene family in maize. Using RNA-seq data, transcriptome analysis indicated that most of ZmWRKY genes displayed differential expression patterns at different developmental stages of maize. Further, by quantitative real-time PCR analysis, twenty-one ZmWRKY genes were confirmed to respond to two different abiotic stress treatments, suggesting their potential roles in various abiotic stress responses. In addition, RNA-seq dataset was used to conduct weighted gene co-expression network analysis (WGCNA) in order to recognize gene subsets possessing similar expression patterns and highly correlated with each other within different metabolic networks. Further, subcellular localization prediction, functional annotation and interaction analysis of ZmWRKY proteins were also performed to predict their interactions and associations involved in potential regulatory network. Conclusions: Taken together, the present study will serve to present an important theoretical basis for further exploring function and regulatory mechanism of ZmWRKY genes in the growth, development, and adaptation to abiotic stresses in maize.

Background: As one of the largest transcription factor families in plants, the APETALA2/Ethylene-Responsive Factor (AP2/ERF) superfamily is involved in various biological processes and plays significant roles in plant growth, development and responses to various stresses. Although identification and characterization of AP2/ERF superfamily genes have been accomplished in many plant species, very little is known regarding the structure and function of AP2/ERF genes in maize. Results: In this study, a total of 214 genes encoding ZmAP2/ERF proteins with complete AP2/ERF domain were eventually identified according to the AGPv4 version of the maize B73 genome. Based on the number of AP2/ERF domain and similarities of amino acid sequences among AP2/ERF proteins from Arabidopsis, rice and maize, all 214 putative ZmAP2/ERF proteins were categorized into three distinct families, including the AP2 family (44), the ERF family (166) and the RAV family (4), respectively. Among them, the ERF family was further subdivided into two diverse subfamilies, including the DREB and ERF subfamilies with 61 and 105 members, respectively. Further, based on phylogenetic analysis, the members of DREB and ERF subfamilies were subdivided into four (Group I-IV) and eight (Group V-XII) groups, respectively. The characteristics of exon-intron structure of these putative ZmAP2/ERF genes and conserved protein motifs of their encoded ZmAP2/ERF proteins were also presented respectively, which was in accordance with the results of group classification. Promoter analysis suggested that ZmAP2/ERF genes shared many stress- and hormone-related cis-regulatory elements. Gene duplication and synteny analysis revealed that tandem or segmental duplication and purifying selection might play significant roles in evolution and functional differentiation of AP2/ERF superfamily genes among three various gramineous species (maize, rice and sorghum). Using RNA-seq data, transcriptome analysis indicated that the majority of ZmAP2/ERF genes displayed differential expression patterns at different developmental stages of maize. In addition, the following analyses of co-expression network among ZmAP2/ERF genes and protein protein interaction between ZmAP2 and ZmERF proteins further enabled us to understand the regulatory relationship among members of the AP2/ERF superfamily in maize. Furthermore, by quantitative real-time PCR analysis, twenty-seven selected ZmAP2/ERF genes were further confirmed to respond to three different abiotic stresses, suggesting their potential roles in various abiotic stress responses. Collectively, these results revealed that these ZmAP2/ERF genes play essential roles in abiotic stress tolerance. Conclusions: Taken together, the present study will serve to present an important theoretical basis for further exploring the function and regulatory mechanism of ZmAP2/ERF genes in the growth, development, and adaptation to abiotic stresses in maize.

The harsh environment such as high temperature greatly limits the growth, development and production of crops worldwide. NAC (NAM, ATAF1/2, and CUC2) transcription factors (TFs) play key regulatory roles in abiotic stress responses of plants. However, the functional roles of NAC TFs in heat stress response of maize remain elusive. In our present study, we identified and isolated a stress-responsive NAC transcription factor gene in maize, designated as ZmNAC074 and orthologous with rice OsNTL3. Further studies revealed that ZmNAC074 may encode a membrane-bound transcription factor (MTF) of NAC family in maize, which is comprised of 517 amino acid residues with a transmembrane domain at the C-terminus. Moreover, ZmNAC074 was highly expressed and induced by various abiotic stresses in maize seedlings, especially in leaf tissues under heat stress. Through generating ZmNAC074 transgenic plants, phenotypic and physiological analyses further displayed that overexpression of ZmNAC074 in transgenic Arabidopsis confers enhanced heat stress tolerance significantly through modulating the accumulation of a variety of stress metabolites, including reactive oxygen species (ROS), antioxidants, malondialdehyde (MDA), proline, soluble protein, chlorophyll and carotenoid. Further, quantitative real-time PCR analysis showed that the expression levels of most ROS scavenging and HSR- and UPR-associated genes in transgenic Arabidopsis were significantly up-regulated under heat stress treatments, suggesting that ZmNAC074 may encode a positive regulator that activates the expression of ROS-scavenging genes and HSR- and UPR-associated genes to enhance plant thermotolerance under heat stress conditions. Overall, our present study suggests that ZmNAC074 may play a crucial role in conferring heat stress tolerance in plants, providing a key candidate regulatory gene for heat stress tolerance regulation and genetic improvement in maize as well as in other crops.

Histone methylation mainly occurs on the lysine residues and plays a crucial role during flowering and stress responses of plants, through changing the methylation status or ratio of lysine residues. Histone lysine residues of plants can arise in three forms of methylation (single, double and triple) and the corresponding demethylation can also ensue on certain occasions, by which the plants can accommodate the homeostasis of histone methylation by means of lysine methyltransferase and demethylase. The JmjC domain-containing proteins, an important family of histone lysine demethylases, play a vital role in maintaining homeostasis of histone methylation in vivo. In this study, we have identified 19 JmjC domain-containing histone demethylase (JHDM) proteins in maize. Based on structural characteristics and a comparison of phylogenetic relationships of JHDM gene families from Arabidopsis, rice and maize, all 19 JHDM proteins in maize were categorized into three different subfamilies. Furthermore, chromosome location and schematic structure revealed an unevenly distribution on chromosomes and structure features of ZmJMJ genes in maize, respectively. Eventually, the 19 ZmJMJ genes displayed different expression patterns at diverse developmental stages of maize based on transcriptome analysis. Further, quantitative real-time PCR analysis showed that all 19 ZmJMJ genes were responsive to heat stress treatment, suggesting their potential roles in heat stress response. Overall, our study will serve to present an important theoretical basis for future functional verification of JHDM genes to further unravel the mechanisms of epigenetic regulation in plants.