title: Gene duplication, exon gain and neofunctionalization of OEP16-related genes in land plants.
abstract: OEP16, a channel protein of the outer membrane of chloroplasts, has been implicated in amino acid transport and in the substrate-dependent import of protochlorophyllide oxidoreductase A. Two major clades of OEP16-related sequences were identified in land plants (OEP16-L and OEP16-S), which arose by a gene duplication event predating the divergence of seed plants and bryophytes. Remarkably, in angiosperms, OEP16-S genes evolved by gaining an additional exon that extends an interhelical loop domain in the pore-forming region of the protein. We analysed the sequence, structure and expression of the corresponding Arabidopsis genes (atOEP16-S and atOEP16-L) and demonstrated that following duplication, both genes diverged in terms of expression patterns and coding sequence. AtOEP16-S, which contains multiple G-box ABA-responsive elements (ABREs) in the promoter region, is regulated by ABI3 and ABI5 and is strongly expressed during the maturation phase in seeds and pollen grains, both desiccation-tolerant tissues. In contrast, atOEP-L, which lacks promoter ABREs, is expressed predominantly in leaves, is induced strongly by low-temperature stress and shows weak induction in response to osmotic stress, salicylic acid and exogenous ABA. Our results indicate that gene duplication, exon gain and regulatory sequence evolution each played a role in the divergence of OEP16 homologues in plants.
authors.affiliation: Plant Molecular Genetics Laboratory, Smurfit Institute of Genetics, Trinity College, Dublin 2, Ireland.
authors.forename: Sinéad C
authors.initials: SC
authors.lastname: Drea
authors.forename: Nga T
authors.initials: NT
authors.lastname: Lao
authors.forename: Kenneth H
authors.initials: KH
authors.lastname: Wolfe
authors.forename: Tony A
authors.initials: TA
authors.lastname: Kavanagh
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D050976:Basic-Leucine Zipper Transcription Factors / Q000235:genetics / Q000502:physiology; D019143:Evolution, Molecular; D005091:Exons; D020440:Gene Duplication; D018506:Gene Expression Regulation, Plant; D007473:Ion Channels / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D012275:Oryza / Q000235:genetics; D018532:Pisum sativum / Q000235:genetics; D010802:Phylogeny; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000378:metabolism; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D012639:Seeds / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D020539:Sequence Analysis, Protein; D012689:Sequence Homology, Nucleic Acid; D014026:Nicotiana / Q000235:genetics; D014157:Transcription Factors
chemical_list: C091601:ABI3 protein, Arabidopsis; C409743:ABI5 protein, Arabidopsis; D029681:Arabidopsis Proteins; D050976:Basic-Leucine Zipper Transcription Factors; D007473:Ion Channels; C512221:OEP16-L protein, Arabidopsis; C512220:OEP16-S protein, Arabidopsis; D014157:Transcription Factors