title: Genome-wide analysis of WRKY gene family in Cucumis sativus.
abstract: BACKGROUND
  WRKY proteins are a large family of transcriptional regulators in higher plant. They are involved in many biological processes, such as plant development, metabolism, and responses to biotic and abiotic stresses. Prior to the present study, only one full-length cucumber WRKY protein had been reported. The recent publication of the draft genome sequence of cucumber allowed us to conduct a genome-wide search for cucumber WRKY proteins, and to compare these positively identified proteins with their homologs in model plants, such as Arabidopsis.
  
  
  RESULTS
  We identified a total of 55 WRKY genes in the cucumber genome. According to structural features of their encoded proteins, the cucumber WRKY (CsWRKY) genes were classified into three groups (group 1-3). Analysis of expression profiles of CsWRKY genes indicated that 48 WRKY genes display differential expression either in their transcript abundance or in their expression patterns under normal growth conditions, and 23 WRKY genes were differentially expressed in response to at least one abiotic stresses (cold, drought or salinity). The expression profile of stress-inducible CsWRKY genes were correlated with those of their putative Arabidopsis WRKY (AtWRKY) orthologs, except for the group 3 WRKY genes. Interestingly, duplicated group 3 AtWRKY genes appear to have been under positive selection pressure during evolution. In contrast, there was no evidence of recent gene duplication or positive selection pressure among CsWRKY group 3 genes, which may have led to the expressional divergence of group 3 orthologs.
  
  
  CONCLUSIONS
  Fifty-five WRKY genes were identified in cucumber and the structure of their encoded proteins, their expression, and their evolution were examined. Considering that there has been extensive expansion of group 3 WRKY genes in angiosperms, the occurrence of different evolutionary events could explain the functional divergence of these genes.
authors.affiliation: Institute of Vegetables and Flowers, Chinese Academy of Agricultural Sciences, 12 Zhongguancun South Street, Beijing, 100081 China.
authors.forename: Jian
authors.initials: J
authors.lastname: Ling
authors.forename: Weijie
authors.initials: W
authors.lastname: Jiang
authors.forename: Ying
authors.initials: Y
authors.lastname: Zhang
authors.forename: Hongjun
authors.initials: H
authors.lastname: Yu
authors.forename: Zhenchuan
authors.initials: Z
authors.lastname: Mao
authors.forename: Xingfang
authors.initials: X
authors.lastname: Gu
authors.forename: Sanwen
authors.initials: S
authors.lastname: Huang
authors.forename: Bingyan
authors.initials: B
authors.lastname: Xie
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics; D002874:Chromosome Mapping; D018553:Cucumis sativus / Q000235:genetics*; D018744:DNA, Plant / Q000235:genetics; D030562:Databases, Protein; D019143:Evolution, Molecular; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D018745:Genome, Plant; D008969:Molecular Sequence Data; D005810:Multigene Family; D020411:Oligonucleotide Array Sequence Analysis; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D014157:Transcription Factors / Q000235:genetics*; D059467:Transcriptome
chemical_list: D018744:DNA, Plant; D010940:Plant Proteins; D014157:Transcription Factors