Constitutive promoter expression in transgenic wheat (Triticum aestivum L.) and sorghum (Sorghum bicolor L.)

Since the first successful wheat (Triticum aestivum L.) transformation in 1993, particle bombardment has become a routine method of delivering foreign DNA into wheat. Sorghum (Sorghum bicolor L. Moench) transformation was also achieved in 1993. Since then there have been few additional reports on the topic. There are many factors that affect particle bombardment\u27s success in obtaining transgenic plants. Particle bombardment parameters, explant tissue and culture, and the choices of DNA constructs are examples of factors that would affect transformation success. The DNA constructs used for effective transformation must have promoters that function properly in the plant it genome for gene expression to occur. In this study, constitutive promoters (rice actin, maize alcohol dehydrogenase, maize ubiquitin, and cauliflower mosaic virus 35S) were evaluated for gene expression in stably transformed wheat callus fines and transiently in sorghum embryonic tissue. The promoters were fused to the uidA (GUS) gene and evaluated for GUS expression by histochemical and chemiluminescent assay in wheat callus and transiently in sorghum embryonic tissue. Histochemical assays were done on the regenerated wheat plants. Position effect, co-suppression, and gene silencing may affect foreign gene expression in stably transformed fines. Although transgene expression is not fully understood, the maize ubiquitin promoter was found to have significantly higher levels of GUS expression than the other three constitutive promoters evaluated in the callus lines. At the whole plant level, the maize ubiquitin promoter expressed GUS in 60% of the transgenic; plants obtained. Expression was considerably lower for the cauliflower mosaic virus 35S, rice actin, and maize alcohol dehydrogenase promoters. Therefore, these findings indicate when a high level of constitutive expression is desired the maize ubiquitin promoter would be an appropriate promoter sequence for a wheat transformation study. Transient GUS activity in embryonic sorghum tissue was found to be very low. It was concluded that there would be a benefit in investigating and isolating new promoter sequences for sorghum transformation