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Molecular and cytogenetic characterization of a transgene locus that induces silencing and methylation of homologous promoters in trans
Author(s) -
Jakowitsch Johannes,
Papp István,
Moscone Eduardo A.,
Van Der Winden Johannes,
Matzke Marjori,
Matzke Antonius J. M.
Publication year - 1999
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1046/j.1365-313x.1999.00357.x
Subject(s) - locus (genetics) , biology , gene silencing , genetics , dna methylation , gene , promoter , transgene , microbiology and biotechnology , gene expression
Summary One type of homology‐dependent gene silencing in transgenic plants involves a silencing locus that is able to transcriptionally inactivate and methylate an unlinked target locus with which it shares sequence identity in promoter regions. In a manner resembling paramutation of endogenous genes, the target locus reactivates and loses methylation progressively over several generations after segregating away from the silencing locus, which autonomously acquires stable methylation. To investigate the origins oftrans‐silencing ability and susceptibility, we have analyzed the structures, flanking DNA sequences and chromosomal locations of a nopaline synthase promoter silencing locus,H 2, and a sensitive target locus,K 81. A partially resistant target locus,K α, has been characterized molecularly. The complex and scrambledH 2locus comprises six copies of the nopaline synthase promoter, two of which are collinear with prokaryotic non‐T‐DNA sequences, and is integrated close to a region of intercalary heterochromatin. These features probably contribute collectively to the silencing ability becauseH 2subclones reintroduced into random locations in the K 81 genome did not frequently induce silencing. Both theK 81andK αloci have simple structures, although the former contains non‐T‐DNA prokaryotic sequences that are also present atH 2, and they are flanked by low copy plant DNA.H 2andK 81might interact effectively because they are present on morphologically similar chromosomes from the T subgenome of allotetraploid tobacco.