The promoter of fatty acid desaturase on chromosome C5 in Brassica napus drives high-level expression in seeds

Abstract

The gene fatty acid desaturase 2 (FAD2) exists in multiple copies in the Brassica napus genome and encodes an enzyme that catalyzes the conversion of oleic acid to linoleic acid. In the present study, we characterized the regulatory region controlling the expression of an FAD2 gene located on chromosome C5 of Brassica napus and named it BnFAD2-C5. A long intron was found within the 5′-untranslated region (5′-UTR) of the BnFAD2-C5 gene. This intron, compared with an intron-less control, conferred up to a sixfold increase in green fluorescent protein (GFP) expression in transgenic Arabidopsis, thus suggesting that it makes function through intron-mediated enhancement. The sequence containing the promoter and intron was identified to promote high levels of gene expression in genital organs, particularly in seeds, using qRT-PCR and transgenic Arabidopsis. We identified the different promoter regions responsible for the tissue-specific gene expression through a deletion analysis of the BnFAD2-C5 promoter and a β-glucuronidase and GFP reporter system. The results showed that the −1020 to −319 bp region primarily controls BnFAD2-C5 gene expression in the root, whereas the −1020 to −581 bp region controls expression in the stem, the −581 to −319 bp region controls expression in the leaf, and the −1257 to −1020 bp region probably controls expression in the floral parts. The −319 to −1 bp region is also important, conferring high-level transcription in the seeds. The transcription of BnFAD2-C5 could be induced by salicylic acid and jasmonic acid, and the relative response elements were identified in the −1257 to −1020 bp region and −319 to −1 bp region, respectively.