A SEED-SPECIFIC BRASSICA-NAPUS OLEOSIN PROMOTER INTERACTS WITH A G-BOX-SPECIFIC PROTEIN AND MAY BE BIDIRECTIONAL

In Brassica napus, oleosins are expressed at high levels in the seed d uring the latter stages of embryo development. The cis-acting regulato ry properties of an 872 bp promoter fragment of a B. napus oleosin gen e were examined by analysis of beta-glucuronidase (GUS) expression in transgenic tobacco plants containing an oleosin promoter-GUS transcrip tional fusion. The reporter gene was expressed at high levels only in seeds, specifically in embryo and endosperm tissue and regulated throu ghout seed development. These data demonstrate that oleosin gene trans cription is regulated in a tissue-specific and temporally regulated ma nner and clearly indicate that oleosin protein expression is co-ordina ted primarily at the transcriptional level. Oleosin mRNA was shown to be abscisic acid (ABA) inducible and an ABA-response element in the ol eosin promoter was shown to be bound by a protein factor in a sequence -specific manner. Sequence analysis of the oleosin promoter has identi fied several other putative cis-acting sequences which may direct oleo sin gene expression. The presence of a large open reading frame in the bottom strand of the oleosin promoter (ORF2) which encodes a polypept ide similar to the ethylene-induced E4 gene of tomato is reported. A P CR-generated DNA probe containing the ORF2 sequence hybridised with a 1.4 kb transcript in total RNA extracts of a variety of tissues, inclu ding leaves and germinated seed cotyledons. This finding suggests that the oleosin gene promoter directs transcription in both directions. I t is the first report of a bi-directional nuclear gene promoter in pla nts.