Stable Transcription Activities Dependent on an Orientation of Tam3 Transposon Insertions intoAntirrhinumand Yeast Promoters Occur Only within Chromatin

Abstract

Transposon insertions occasionally occur in the promoter regions of plant genes, many of which are still capable of being transcribed. However, it remains unclear how transcription of such promoters is able to occur. Insertion of the Tam3 transposon into various genes of Antirrhinum majus can confer leaky phenotypes without its excision. These genes, named Tam3-permissible alleles, often contain Tam3 in their promoter regions. Two alleles at different anthocyanin biosynthesis loci, nivea recurrens::Tam3 (niv rec ) and pallida recurrens::Tam3 (pal rec ), both contain Tam3 at a similar position immediately upstream of the promoter TATA-box; however, these insertions had different phenotypic consequences. Under conditions where the inserted Tam3 is immobilized, the niv rec line produces pale red petals, whereas the pal rec line produces no pigment. These pigmentation patterns are correlated with the level of transcripts from the niv rec or pal rec alleles, and these transcriptional activities are independent of DNA methylation in their promoter regions. In niv rec , Tam3 is inserted in an orientation that results in the 3# end of Tam3 adjacent to the 5# region of the gene coding sequence. In contrast, the pal rec allele contains a Tam3 insertion in the opposite orientation. Four of five different nonrelated genes that are also Tam3-permissible alleles and contain Tam3 within the promoter region share the same Tam3 orientation as niv rec . The different transcriptional activities dependent on Tam3 orientation in the Antirrhinum promoters were consistent with expression of luciferase reporter constructs introduced into yeast chromosomes but not with transient expression of these constructs in Antirrhinum cells. These results suggest that for Tam3 to sustain stable transcriptional activity in various promoters it must be embedded in chromatin.

A pair of transposons coordinately suppresses gene expression, independent of pathways mediated by siRNA in Antirrhinum

“…The niv rec allele carrying the upstream Tam3 exhibited a leaky phenotype, because the 3′ end region of Tam3 adapts any promoter sequence for limited expression of the gene (Uchiyama et al ., ). In fact, leaky phenotypes in Antirrhinum have been described in several loci where Tam3 was inserted in the same orientation as the downstream gene; a reporter gene with Tam3 in the promoter sequence validated this finding in yeast (Uchiyama et al ., ). These alleles, called ‘Tam3‐permissible alleles’, seem to be ubiquitous for the expression of any genes (Uchiyama et al ., ).…”

“…In fact, leaky phenotypes in Antirrhinum have been described in several loci where Tam3 was inserted in the same orientation as the downstream gene; a reporter gene with Tam3 in the promoter sequence validated this finding in yeast (Uchiyama et al ., ). These alleles, called ‘Tam3‐permissible alleles’, seem to be ubiquitous for the expression of any genes (Uchiyama et al ., ).…”

“…The occurrence of the different phenotypes in suppressible alleles described for Spm and Mu elements in maize depends on the presence/absence of their TPases (autonomous elements), although the background petal pigmentation driven by the niv rec allele in HAM2 was not related to transcription and translation of the Tam3 TPase gene (Uchiyama et al ., , ). Thus, niv regulation as a result of Tam3 is apparently distinct from that occurring in the suppressible alleles of Spm and Mu in maize.…”

Transposons and Gene Creation

“…In Antirrhinum, the hAT element Tam3 is inserted into the promoters of several genes, creating what has been termed Tam3-permissible gene expression (Uchiyama et al, 2009). In these alleles, sequences in the 3 end of the Tam3 element, rich in AA, TA, and TT dinucleotides, may be involved in positioning nucleosomes on the promoter of the target gene.…”

The backstage of the ABC model: TheAntirrhinum majuscontribution

“…Precise and imprecise transposon excision events were extensively used to explore cell -cell communication and cis-regulatory elements (Coen et al 1986;Sommer et al 1988). In the A. majus genome, at least 11 active "cut and paste" transposons were recognised and they represent an incredible genetic tool to obtain mutants (Schwarz-Sommer et al 2003;Uchiyama et al 2009). Transposon-tagging systems were extensively used to identify the genes controlling flower development, floral-organ identity and inflorescence architecture.…”