DEVELOPMENT OF A BINARY VECTOR SYSTEM FOR PLANT TRANSFORMATION BASED ON THE SUPERVIRULENT AGROBACTERIUM-TUMEFACIENS STRAIN CHRY5

This report describes the disarming of Agrobacterium tumefaciens Chry5 , a strain highly tumorigenic on soybean. Disarming was achieved by re moving an approximately 16.5-kb segment of the 285-kb Ti plasmid pTiCh ry5, including approximately 4 kb of the oncogenic T-DNA and an extend ed region right of the T-DNA, and replacing it with a gene for carbeni cillin resistance, through homologous recombination. The deletion was confirmed with Southern analysis, and the loss of tumorigenicity was v erified in tobacco and tomato plant stem inoculation assays. The delet ion mutant, named KYRT1, successfully transferred the beta-glucuronida se (GUS) gene into tobacco leaf tissue, producing GUS-expressing callu s which could be regenerated into viable plants. In a comparative stud y, the transformation efficiency of A. tumefaciens KYRT1, GV3850, and EHA105 was assayed by inoculating cotyledonary node explants. The resu lts of this study revealed that, in a binary vector system, KYRT1 is e qually or more effective than EHA105 or GV3850 at delivering DNA into soybean.