Isolation of a Polyubiquitin Promoter and Its Expression in Transgenic Potato Plants

Open Access
Publisher Website
Google Scholar
Abstract
A polyubiquitin clone (ubi7) was isolated from a potato (Solanum tuberosum) genomic library using a copy-specific probe from a stress-induced ubiquitin cDNA. The genomic clone contained a 569-bp intron immediately 5[prime] to the initiation codon for the first ubiquitin-coding unit. Two chimeric [beta]-glucuronidase (GUS) fusion transgenes were introduced into potato. The first contained GUS fused to a 1156-bp promoter fragment containing only 5[prime] flanking and 5[prime] untranslated sequences from ubi7. The second transgene contained GUS translationally fused to the carboxy terminus of the first ubiquitin-coding unit and thus included the intron present in the 5[prime] untranslated region of the polyubiquitin gene. Both ubi7-GUS transgenes were activated by wounding in tuber tissue and in leaves by application of exogenous methyl jasmonate. They were also expressed constitutively in the potato tuber peel (outer 1–2 mm). Both transgenes were actively expressed in mature leaves. Exceptionally high levels of expression were observed in senescent leaves. Transgenic clones containing the ubi7 intron and the first ubiquitin-coding unit showed GUS expression levels at least 10 times higher than clones containing GUS fused to the intronless promoter.