Promoters for pregenomic RNA of banana streak badnavirus are active for transgene expression in monocot and dicot plants

Two putative promoters from Australian banana streak badnavirus (BSV) isola tes were analysed for activity in different plant species. In transient exp ression systems the My (2105 bp) and Cv (1322 bp) fragments were both shown to have promoter activity in a wide range of plant species including monoc ots (maize, barley, banana, millet, wheat, sorghum), dicots (tobacco, canol a, sunflower, Nicotiana benthamiana, tipu tree), gymnosperm (Pinus radiata) and fern (Nephrolepis cordifolia). Evaluation of the My and Cv promoters i n transgenic sugarcane, banana and tobacco plants demonstrated that these p romoters could drive high-level expression of either the green fluorescent protein (GFP) or the beta -glucuronidase (GUS) reporter gene (uidA) in vege tative plant cells. In transgenic sugarcane plants harbouring the Cv promot er, GFP expression levels were comparable or higher (up to 1.06% of total s oluble leaf protein as GFP) than those of plants containing the maize ubiqu itin promoter (up to 0.34% of total soluble leaf protein). GUS activities i n transgenic in vitro-grown banana plants containing the My promoter were u p to seven-fold stronger in leaf tissue and up to four-fold stronger in roo t and corm tissue than in plants harbouring the maize ubiquitin promoter. T he Cv promoter showed activities that were similar to the maize ubiquitin p romoter in in vitro-grown banana plants, but was significantly reduced in l arger glasshouse-grown plants. In transgenic in vitro-grown tobacco plants, the My promoter reached activities close to those of the 35S promoter of c auliflower mosaic virus (CaMV), while the Cv promoter was about half as act ive as the CaMV 35S promoter. The BSV promoters for pregenomic RNA represen t useful tools for the high-level expression of foreign genes in transgenic monocots.