Abstract
BackgroundHeat shock response in eukaryotes is transcriptionally regulated by conserved heat shock transcription factors (Hsfs). Hsf genes are represented by a large multigene family in plants and investigation of the Hsf gene family will serve to elucidate the mechanisms by which plants respond to stress. In recent years, reports of genome-wide structural and evolutionary analysis of the entire Hsf gene family have been generated in two model plant systems, Arabidopsis and rice. Maize, an important cereal crop, has represented a model plant for genetics and evolutionary research. Although some Hsf genes have been characterized in maize, analysis of the entire Hsf gene family were not completed following Maize (B73) Genome Sequencing Project.ResultsA genome-wide analysis was carried out in the present study to identify all Hsfs maize genes. Due to the availability of complete maize genome sequences, 25 nonredundant Hsf genes, named ZmHsfs were identified. Chromosomal location, protein domain and motif organization of ZmHsfs were analyzed in maize genome. The phylogenetic relationships, gene duplications and expression profiles of ZmHsf genes were also presented in this study. Twenty-five ZmHsfs were classified into three major classes (class A, B, and C) according to their structural characteristics and phylogenetic comparisons, and class A was further subdivided into 10 subclasses. Moreover, phylogenetic analysis indicated that the orthologs from the three species (maize, Arabidopsis and rice) were distributed in all three classes, it also revealed diverse Hsf gene family expression patterns in classes and subclasses. Chromosomal/segmental duplications played a key role in Hsf gene family expansion in maize by investigation of gene duplication events. Furthermore, the transcripts of 25 ZmHsf genes were detected in the leaves by heat shock using quantitative real-time PCR. The result demonstrated that ZmHsf genes exhibit different expression levels in heat stress treatment.ConclusionsOverall, data obtained from our investigation contributes to a better understanding of the complexity of the maize Hsf gene family and provides the first step towards directing future experimentation designed to perform systematic analysis of the functions of the Hsf gene family.
Highlights
Heat shock response in eukaryotes is transcriptionally regulated by conserved heat shock transcription factors (Hsfs)
In the nine duplicated gene pairs of maize, the significant divergence of expression levels between the two members of each gene pair implied that duplicated genes had various functions in the response to heat stress in the evolutionary history. This survey presents a comprehensive overview of the Hsf gene family repertoire within the maize draft genome
Based on structural characteristics and a comparison of the phylogenetic relationships among maize, rice, and Arabidopsis, all 25 ZmHsfs fell into three major classes, and class A was organized into 10 subclasses
Summary
Heat shock response in eukaryotes is transcriptionally regulated by conserved heat shock transcription factors (Hsfs). All organisms possess an evolutionarily conserved, rapid cellular defense mechanism commonly designated as the heat shock (HS) response, which activates a variety of reactions in response to heat stress and a number of chemical stressors. It is characterized by rapid reprogramming of gene expression, leading to the production of a defined set of proteins called heat shock proteins (Hsps), most of which act as molecular chaperones [1,2]. In response to heat shock, Hsf is converted from a transcriptional inactive monomer to active trimmer using oligomerization domains, which function as sequencespecific trimeric DNA binding proteins. At least three 5’-nGAAn-3’ repeats are required for a functional HSE, and additional reiteration of the pentameric unit results in higher affinity interactions between Hsf and HSE [7]
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