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A transgene with repeated DNA causes high frequency, post‐transcriptional suppression of ACC‐oxidase gene expression in tomato
Author(s) -
Hamilton Andrew J.,
Brown Stephen,
Yuanhai Han,
Ishizuka Masakatsu,
Lowe Alex,
Solis AngelGabriel Alpuche,
Grierson Don
Publication year - 1998
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.1998.00251.x
Subject(s) - transgene , gene silencing , biology , gene , sense (electronics) , microbiology and biotechnology , gene expression , genetically modified rice , endogeny , untranslated region , exon , intron , rna interference , genetics , rna , genetically modified crops , biochemistry , chemistry
Summary Gene silencing with sense genes is an important method for down‐regulating the expression of endogenous plant genes, but the frequency of silencing is unpredictable. Fifteen per cent of tomato plants transformed with a 35S‐ACC‐oxidase (ACO1) sense gene had reduced ACC‐oxidase activity. However, 96% of plants transformed with an ACC‐oxidase sense gene, containing two additional upstream inverted copies of its 5′ untranslated region, exhibited reduced ACC‐oxidase activity compared to wild‐type plants. In the three plants chosen for analysis, there were substantially reduced amounts of both endogenous and transgenic ACO RNA, indicating that this was an example of co‐suppression. Ribonuclease protection assays using probes spanning intron‐exon borders showed that the reduced accumulation of endogenous ACO mRNA occurred post‐transcriptionally since the abundance of unprocessed transcripts was not affected. TheACO1transgene with the repeated 5′UTR also strongly inhibited the accumulation of RNA from the relatedACO2 gene in flowers, although there is little homology between the 5′UTRs ofACO1 andACO2. These results indicate that although repeated DNA in a transgene greatly enhances the probability of gene silencing of an endogenous gene, it also involves generation of atrans‐acting silencing signal produced, at least partly, from sequences external to the repeat.