, Volume 7, Issue 3, pp 165-172

Heterologous and homologous transgenic expression directed by a 2S seed storage promoter of Brassica napus

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Abstract

Few plant genes have been analysed in both homologous and heterologous transgenic systems. In this study, deletion mutants of the storage protein promoter napA fused to the receptor gene uidA (GUS) were analysed for their ability to direct tissue-specific expres sion in transgenic tobacco as well as transgenic Brassica napus. In seeds, qualitatively similar results have previously been obtained, demonstrating that transcription factors in the heterologous tobacco system recognized the napA promoter cis elements, more or less in the same way as in B. napus (Ellerstrom et al., 1996; Stalberg et al., 1996). However, in anthers of the transgenic plants, clear differences were noted. The napA promoter constructs were inactive in transgenic B. napus anthers. In contrast, tobacco anthers displayed activities of similar magnitudes to those previously found in the seed for the respective promoter constructs. Interestingly, in seven constructs the activity in the anthers was retained dow nstream from an imperfect ABRE element, whereas no activity could be detected in the seed. Another clear difference was that a region from −211 to −152 silenced the expression in anthers whereas this region had no effect on the activity in the seed. Likewise, in tobacco the napA promoter showed a low activity in leaves. Histochemical staining of young tobacco leaves showed that this activity was considerably higher in stomata guard cells than in the mesophyll cells while the leaves of the B. napus plants had a diffuse and barely detectable staining in the mesophyll cells. The high level of napA transcription in tobacco anthers indicates that the set of transcription factors and corresponding cis-sequences that direct tissue-specific transcription in this organ are similar to those responsible for seed-specific expression. However, comparison of the levels of expression in anthers and seeds in individual plants revealed that there was no correlation between the activities in the two organs, which suggests that positional effects influence the transcription complexes differently in seeds and anthers. Further, this study shows that careful analysis of expression directed by promoter mutants in a heterologous transformation system might reveal important cis-elements, not discernible in the tighter homologous situation