Genome-wide identification and analysis of WRKY gene family in maize provide insights into regulatory network in response to abiotic stresses.

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.

Genome-wide identification, classification and expression analysis of the Hsf and Hsp70 gene families in maize.

Heat shock factors (Hsfs) and heat shock proteins (Hsps) play a critical role in the molecular mechanisms such as plant development and defense against abiotic. As an important food crop, maize is vulnerable to adverse environment such as heat stress and water logging, which leads to a decline in yield and quality. To date, very little is known regarding the structure and function of Hsf and Hsp genes in maize. Although some Hsf and Hsp genes have been characterized in maize, analysis of the entire Hsf and Hsp70 gene families were not completed following Maize (B73) Genome Sequencing Project. Therefore, studying their molecular mechanism and revealing their biological function in plant stress resistance process will contribute to reveal important theoretical significance and application value for improving corn yield and quality. In this study, we have identified 25 ZmHsf and 22 ZmHsp70 genes in maize. The structural characteristics and phylogenetic relationships of the Hsf and Hsp70 gene families of Arabidopsis thaliana, rice and maize were compared. The final 25 ZmHsf proteins and 22 ZmHsp70 proteins were divided into three and four subfamilies, respectively. In addition, chromosomal localization indicated that the ZmHsf and ZmHsp70 genes were unevenly distributed on the chromosome, and the gene structure map revealed the characteristics of their structures. Finally, transcriptome analysis indicated that most of the ZmHsf and ZmHsp70 genes showed different expression patterns at different developmental stages of maize. Further, by semi-quantitative RT-PCR and quantitative real-time PCR analysis, all 25 ZmHsf and 22 ZmHsp70 genes were confirmed to respond to heat stress treatment, indicating that they have potential effects in heat stress response. The analyses performed by combining co-expression network with protein-protein interaction network among the members of the Hsf and Hsp70 gene families in maize further enabled us to recognize components involved in the regulatory network associated with hsfs and hsp70s complex. The predicted subcellular location revealed that maize Hsp70 proteins exhibited a various subcellular distribution, which may be associated with functional diversification in heat stress response. Taken together, our study provides comprehensive information on the members of Hsf and Hsp70 gene families and will help in elucidating their exact function in maize.

Genome-wide identification, classification and expression analysis of the JmjC domain-containing histone demethylase gene family in maize.

BACKGROUND: 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. RESULTS: 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. CONCLUSIONS: 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.

The Dynamics of DNA methylation in the maize (Zea mays L.) inbred line B73 response to heat stress at the seedling stage.

High temperature stress has become a major concern for crop production worldwide because it greatly affects the growth, development, and productivity of plants. The mechanisms underlying the development of heat-tolerance need to be better understood for important agricultural crops. Recent research shows that DNA methylation is dynamic during plant development. However, the molecular mechanism regulating these dynamic DNA methylation patterns remains to be elucidated. In this study, six MethylRAD libraries were constructed using DNA isolated from leaves of maize. A total of 42,561,144 and 48,157,284 clean reads were generated from CK (Control condition) and HTP (Heat stress condition) treatments, respectively. The results showed that a total of 25,470 methylated genes were found in six tested samples, including 325 differentially methylated genes (200 in CCGG sites and 125 in CCWGG sites) between the CK and HTP samples. KEGG pathway enrichment analysis for DMGs indicated that Spliceosome, Homologous recombination, RNA transport, Ubiquitin mediated proteolysis and Carbon metabolism pathways play a central role in maize response to heat stress. Taken together, this research revealed the genome-wide DNA methylation pattern of maize leaves in response to heat exposure and identified candidate genes potentially involved in response to heat stress at the methylation level, which will facilitate future studies to elucidate the epigenetic mechanisms underlying the responses of maize to heat stress.

Transcriptomic analysis of the maize (Zea mays L.) inbred line B73 response to heat stress at the seedling stage.

High temperature is a common stress, which influences the growth and reproduction of plants. Maize is one of the most important crops all over the world. However, heat stress reduces significantly the yield and quality of maize. Therefore, it is important to illuminate molecular mechanism of maize response to heat stress. To estimate genes related to heat stress, we analyzed the transcriptome of maize in response to heat stress. In this study, six cDNA libraries were constructed form total RNA isolated from leaves of maize. A total of 35,209,446 and 35,205,472 clean reads were generated from CK (Control condition) and HTP (Heat stress condition) treatments, respectively. The results showed that 1857 DEGs were identified in maize after heat stress (1029 up-regulated and 828 down-regulated). KEGG pathway enrichment analysis for DEGs indicated that protein processing in endoplasmic reticulum pathways play a central role in maize response to heat stress. In addition, in the present study, 167 putative TFs were identified, which belong to various TF families (e.g., MYB, AP2-EREBP, b-ZIP, bHLH, NAC and WRKY), and may be associated with heat stress response of maize. This research may contribute to understand the molecular mechanism of maize inbred line B73 response to heat stress, which is beneficial for developing maize cultivars to improve yield and quality.