Abstract:

A novel selective system ideal for plant transformation was introduced. The system uses Escherichia coli phosphomannose isomerase(PMI) gene as the selectable marker gene and mannose as the selective agent.PMI is an enzyme catalyzing the conversion of mannose-6-phosphate to fructose-6-phosphate;the latter can be further metabolized in glycolysis.Transformed cells can grow normally utilizing mannose as carbon source,while non-transformed cells cannot because of non_metabolizable nature of mannose-6-phosphate.The transformation frequency was affected by genotypes,sugars other than mannose,concentrations of phosphate and culture conditions.The system has been evaluated in woody plants,sweet orange and grape,as well as in annual crops and is regarded to be an ideal replacement for traditional antibiotic or herbicide selective systems.Besides general methods for detecting transgenic plants,plants transformed with PMI gene can be assayed by enzyme activity analyses. Especially,the chlorophenol red (CPR) method for PMI activity analysis is simple,reliable,and need no expensive reagents.The plants transformed with PMI gene were demonstrated to be safe to human health and environment.All the results indicate that PMI is an effective selective marker for plant transformation.

Key words: phosphomannose isomerase(PMI) gene, mannose, plant, genetic transformation