title: Retrotransposon BARE displays strong tissue-specific differences in expression.
abstract: The BARE retrotransposon comprises c. 10% of the barley (Hordeum vulgare) genome. It is actively transcribed, translated and forms virus-like particles (VLPs). For retrotransposons, the inheritance of new copies depends critically on where in the plant replication occurs. In order to shed light on the replication strategy of BARE in the plant, we have used immunolocalization and in situ hybridization to examine expression of the BARE capsid protein, Gag, at a tissue-specific level. Gag is expressed in provascular tissues and highly localized in companion cells surrounding the phloem sieve tubes in mature vascular tissues. BARE Gag and RNA was not seen in the shoot apical meristem of young seedlings, but appeared, following transition to flowering, in the developing floral spike. Moreover, Gag has a highly specific localization in pre-fertilization ovaries. The strong presence of Gag in the floral meristems suggests that newly replicated copies there will be passed to the next generation. BARE expression patterns are consistent with transcriptional regulation by predicted response elements in the BARE promoter, and in the ovary with release from epigenetic transcriptional silencing. To our knowledge, this is the first analysis of the expression of native retrotransposon proteins within a plant to be reported.
authors.affiliation: MTT/BI Plant Genomics Laboratory, Institute of Biotechnology, Viikki Biocenter, University of Helsinki, PO Box 65, Viikinkaari 1, FIN-00014, Helsinki, Finland.
authors.forename: Marko
authors.initials: M
authors.lastname: Jääskeläinen
authors.forename: Wei
authors.initials: W
authors.lastname: Chang
authors.forename: Cédric
authors.initials: C
authors.lastname: Moisy
authors.forename: Alan H
authors.initials: AH
authors.lastname: Schulman
mesh_terms: D036022:Capsid Proteins / Q000378:metabolism; D055864:Droughts; D018506:Gene Expression Regulation, Plant; D015683:Gene Products, gag / Q000235:genetics / Q000378:metabolism; D001467:Hordeum / Q000235:genetics*; D015151:Immunoblotting; D018519:Meristem / Q000235:genetics; D008969:Molecular Sequence Data; D009928:Organ Specificity / Q000235:genetics*; D063245:Plant Development / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D058526:Plant Vascular Bundle / Q000235:genetics; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D012194:RNA-Directed DNA Polymerase / Q000235:genetics / Q000378:metabolism; D018626:Retroelements / Q000235:genetics*; D012639:Seeds / Q000235:genetics
chemical_list: D036022:Capsid Proteins; D015683:Gene Products, gag; D010940:Plant Proteins; D018749:RNA, Plant; D018626:Retroelements; D012194:RNA-Directed DNA Polymerase
keywords: Gag; Hordeum vulgare (barley); immunolocalization; retrotransposon replication; translation