A transformation method for obtaining marker-free plants based on phosphomannose isomerase

A selectable marker system for plant transformation of rape plants that does not require the use of antibiotics or herbicides was developed. The selectable marker consists of the phosphomannose isomerase (PMI) gene from E. coli under the control of a plant promoter. The PMI gene was transferred to Brassica napus by Agrobacterium- mediated transformation, which allows the selection of transgenic plants with mannose and sucrose as selective agents. The highest transformation frequency of 7.9 % was obtained when a combination of 4.5 g l -1 mannose and 10 g l -1 sucrose was used. For early identifi cation of transgenic events, histochemical staining with 5-bromo-4-chloro3-indolyl-s 3-indolyl-s 3-indolyl- -D-glucuronide (X-Gluc) was used. Stable integration of the transgene was confi rmed by PCR and Southern blot analysis. These preliminary results indicate that the mannose selection system can be used for Agrobacterium-mediated transformation of rape plants.