title: The frequent transcriptional readthrough of the tobacco Tnt1 retrotransposon and its possible implications for the control of resistance genes.
abstract: Retrotransposons are a major component of eukaryote genomes, being especially abundant in plant genomes. They are frequently found inserted in gene-rich regions and have greatly contributed to the evolution of gene coding capacity and regulation. Retrotransposon insertions can influence the expression of neighboring genes in many ways, such as modifying their promoter or terminator sequences and altering their epigenetic control. Plant retrotransposons are highly regulated and their expression is usually associated with stress situations. While the control of transcription of some plant retrotransposons has been analyzed in some detail, little is known about the transcriptional termination of these elements. Here we show that the transcripts of the tobacco retrotransposon Tnt1 display a high variability of polyadenylation sites, only a fraction of them terminating at the major termination site. We also report on the ability of Tnt1 to extend its transcription into flanking genomic sequences and we analyze a particular case in which Tnt1 transcripts include sequences of an oppositely oriented resistance-like gene. The expression of this gene and the neighboring Tnt1 copy generate transcripts overlapping in more that 800 nucleotides, which could anneal and form dsRNAs and enter into silencing regulatory pathways. Resistance gene loci are usually composed of tandem arrays of resistance-like genes, a number of which contain mutations, including retrotransposon insertions, and are considered as to be pseudogenes. Given that plant retrotransposons are usually regulated by stress, the convergent expression of these resistance-like pseudogenes and the interleaving inducible retrotransposons may contribute to the control of plant responses to stress.
authors.affiliation: Centre de Recerca en Agrigenòmica (CRAG), CSIC-IRTA-UAB, Institut de Biología Molecular de Barcelona (IBMB-CSIC), Jordi Girona 18, 08034, Barcelona, Spain.
authors.forename: Inmaculada
authors.initials: I
authors.lastname: Hernández-Pinzón
authors.forename: Erika
authors.initials: E
authors.lastname: de Jesús
authors.forename: Néstor
authors.initials: N
authors.lastname: Santiago
authors.forename: Josep M
authors.initials: JM
authors.lastname: Casacuberta
mesh_terms: D001483:Base Sequence; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D049452:Green Fluorescent Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D050436:Regulatory Elements, Transcriptional / Q000235:genetics; D012045:Regulatory Sequences, Nucleic Acid; D018626:Retroelements / Q000235:genetics* / Q000502:physiology; D013312:Stress, Physiological / Q000235:genetics; D020079:Terminal Repeat Sequences / Q000235:genetics; D014026:Nicotiana / Q000235:genetics*; D014158:Transcription, Genetic
chemical_list: D018626:Retroelements; D049452:Green Fluorescent Proteins