title: Systematic analysis of sequences and expression patterns of drought-responsive members of the HD-Zip gene family in maize.
abstract: BACKGROUND
  Members of the homeodomain-leucine zipper (HD-Zip) gene family encode transcription factors that are unique to plants and have diverse functions in plant growth and development such as various stress responses, organ formation and vascular development. Although systematic characterization of this family has been carried out in Arabidopsis and rice, little is known about HD-Zip genes in maize (Zea mays L.).
  
  
  RESULTS
  In this study, we described the identification and structural characterization of HD-Zip genes in the maize genome. A complete set of 55 HD-Zip genes (Zmhdz1-55) were identified in the maize genome using Blast search tools and categorized into four classes (HD-Zip I-IV) based on phylogeny. Chromosomal location of these genes revealed that they are distributed unevenly across all 10 chromosomes. Segmental duplication contributed largely to the expansion of the maize HD-ZIP gene family, while tandem duplication was only responsible for the amplification of the HD-Zip II genes. Furthermore, most of the maize HD-Zip I genes were found to contain an overabundance of stress-related cis-elements in their promoter sequences. The expression levels of the 17 HD-Zip I genes under drought stress were also investigated by quantitative real-time PCR (qRT-PCR). All of the 17 maize HD-ZIP I genes were found to be regulated by drought stress, and the duplicated genes within a sister pair exhibited the similar expression patterns, suggesting their conserved functions during the process of evolution.
  
  
  CONCLUSIONS
  Our results reveal a comprehensive overview of the maize HD-Zip gene family and provide the first step towards the selection of Zmhdz genes for cloning and functional research to uncover their roles in maize growth and development.
authors.affiliation: Key Laboratory of Crop Biology of Anhui Province, Anhui Agricultural University, Hefei, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Zhao
authors.forename: Yuqiong
authors.initials: Y
authors.lastname: Zhou
authors.forename: Haiyang
authors.initials: H
authors.lastname: Jiang
authors.forename: Xiaoyu
authors.initials: X
authors.lastname: Li
authors.forename: Defang
authors.initials: D
authors.lastname: Gan
authors.forename: Xiaojian
authors.initials: X
authors.lastname: Peng
authors.forename: Suwen
authors.initials: S
authors.lastname: Zhu
authors.forename: Beijiu
authors.initials: B
authors.lastname: Cheng
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics; D001483:Base Sequence; D002874:Chromosome Mapping / Q000379:methods; D017124:Conserved Sequence; D055864:Droughts; D018506:Gene Expression Regulation, Plant; D018745:Genome, Plant; D016350:Leucine Zippers / Q000235:genetics*; D008390:Markov Chains; D008969:Molecular Sequence Data; D012275:Oryza / Q000235:genetics; D010802:Phylogeny; D011401:Promoter Regions, Genetic; D060888:Real-Time Polymerase Chain Reaction / Q000379:methods; D014158:Transcription, Genetic; D003313:Zea mays / Q000235:genetics*