title: Cis-regulatory signatures of orthologous stress-associated bZIP transcription factors from rice, sorghum and Arabidopsis based on phylogenetic footprints.
abstract: BACKGROUND
  The potential contribution of upstream sequence variation to the unique features of orthologous genes is just beginning to be unraveled. A core subset of stress-associated bZIP transcription factors from rice (Oryza sativa) formed ten clusters of orthologous groups (COG) with genes from the monocot sorghum (Sorghum bicolor) and dicot Arabidopsis (Arabidopsis thaliana). The total cis-regulatory information content of each stress-associated COG was examined by phylogenetic footprinting to reveal ortholog-specific, lineage-specific and species-specific conservation patterns.
  
  
  RESULTS
  The most apparent pattern observed was the occurrence of spatially conserved 'core modules' among the COGs but not among paralogs. These core modules are comprised of various combinations of two to four putative transcription factor binding site (TFBS) classes associated with either developmental or stress-related functions. Outside the core modules are specific stress (ABA, oxidative, abiotic, biotic) or organ-associated signals, which may be functioning as 'regulatory fine-tuners' and further define lineage-specific and species-specific cis-regulatory signatures. Orthologous monocot and dicot promoters have distinct TFBS classes involved in disease and oxidative-regulated expression, while the orthologous rice and sorghum promoters have distinct combinations of root-specific signals, a pattern that is not particularly conserved in Arabidopsis.
  
  
  CONCLUSIONS
  Patterns of cis-regulatory conservation imply that each ortholog has distinct signatures, further suggesting that they are potentially unique in a regulatory context despite the presumed conservation of broad biological function during speciation. Based on the observed patterns of conservation, we postulate that core modules are likely primary determinants of basal developmental programming, which may be integrated with and further elaborated by additional intrinsic or extrinsic signals in conjunction with lineage-specific or species-specific regulatory fine-tuners. This synergy may be critical for finer-scale spatio-temporal regulation, hence unique expression profiles of homologous transcription factors from different species with distinct zones of ecological adaptation such as rice, sorghum and Arabidopsis. The patterns revealed from these comparisons set the stage for further empirical validation by functional genomics.
authors.affiliation: School of Biology and Ecology, University of Maine, 5735 Hitchner Hall, Orono, ME 04469, USA.
authors.forename: Fuyu
authors.initials: F
authors.lastname: Xu
authors.forename: Myoung-Ryoul
authors.initials: MR
authors.lastname: Park
authors.forename: Ai
authors.initials: A
authors.lastname: Kitazumi
authors.forename: Venura
authors.initials: V
authors.lastname: Herath
authors.forename: Bijayalaxmi
authors.initials: B
authors.lastname: Mohanty
authors.forename: Song Joong
authors.initials: SJ
authors.lastname: Yun
authors.forename: Benildo G
authors.initials: BG
authors.lastname: de los Reyes
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics; D017360:Arabidopsis / Q000235:genetics*; D001483:Base Sequence; D050976:Basic-Leucine Zipper Transcription Factors / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D001665:Binding Sites; D017124:Conserved Sequence; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D005810:Multigene Family; D012275:Oryza / Q000235:genetics*; D010802:Phylogeny; D010940:Plant Proteins / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012689:Sequence Homology, Nucleic Acid; D045868:Sorghum / Q000235:genetics*; D013045:Species Specificity; D013312:Stress, Physiological / Q000235:genetics
chemical_list: D050976:Basic-Leucine Zipper Transcription Factors; D010940:Plant Proteins