title: Post-transcriptional regulation of phenylalanine ammonia-lyase expression in tobacco following recovery from gene silencing.
abstract: Introduction of a bean phenylalanine ammonia-lyase (PAL) transgene into tobacco plants results in epigenetic post-transcriptional gene silencing which is unstable, such that after self-pollination first generation progeny may become PAL over-expressors. The change from gene silencing to PAL over-expression is accompanied by a loss of cytosine methylation of the PAL transgene and reduced methylation of the endogenous tobacco PAL2 gene, but not the PAL1 gene. These changes are associated with the appearance of high levels of bean PAL and tobacco PAL2 transcripts in the total RNA fraction from PAL over-expressing plants. However, tobacco PAL2 transcripts are inefficiently recruited into polysomes, and tobacco PAL2 protein is not detected in leaves of PAL over-expressing or wild-type lines. Thus, in spite of the post-transcriptionally controlled increase in tobacco PAL2 transcripts in PAL over-expressors, the increased PAL activity is primarily the result of the increase in bean PAL transcripts and corresponding enzymatic activity. These results reveal a complex cross-talk between expression of the PAL transgene and the corresponding endogenous PAL genes at the levels of transcription, transcript stability and polysomal recruitment during sense transgene-mediated silencing and subsequent over-expresson of PAL in tobacco.
authors.affiliation: Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, Oklahoma 73401, USA.
authors.forename: J T
authors.initials: JT
authors.lastname: Reddy
authors.forename: K L
authors.initials: KL
authors.lastname: Korth
authors.forename: S V
authors.initials: SV
authors.lastname: Wesley
authors.forename: P A
authors.initials: PA
authors.lastname: Howles
authors.forename: S
authors.initials: S
authors.lastname: Rasmussen
authors.forename: C
authors.initials: C
authors.lastname: Lamb
authors.forename: R A
authors.initials: RA
authors.lastname: Dixon
mesh_terms: D019175:DNA Methylation / Q000187:drug effects; D007887:Fabaceae / Q000201:enzymology / Q000235:genetics; D005786:Gene Expression Regulation; D020868:Gene Silencing; D017343:Genes, Plant / Q000235:genetics; D010650:Phenylalanine Ammonia-Lyase / Q000235:genetics* / Q000378:metabolism / Q000494:pharmacology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D030821:Plants, Genetically Modified; D010946:Plants, Medicinal; D010947:Plants, Toxic; D011132:Polyribosomes / Q000235:genetics; D012313:RNA / Q000187:drug effects / Q000378:metabolism; D015347:RNA Probes / Q000138:chemical synthesis; D012323:RNA Processing, Post-Transcriptional; D020871:RNA Stability / Q000187:drug effects; D014026:Nicotiana / Q000201:enzymology / Q000235:genetics*; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D010940:Plant Proteins; D015347:RNA Probes; D012313:RNA; D010650:Phenylalanine Ammonia-Lyase