Characterization of a new Agrobacterium tumefaciens strain from alfalfa (Medicago sativa L.)
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© Springer-Verlag 1998
O R I G I N A L PA P E R
Jeffrey D. Palumbo · Donald A. Phillips · Clarence I. Kado
Characterization of a new Agrobacterium tumefaciens strain from alfalfa (Medicago sativa L.)
Received: 17 October 1997 / Accepted: 8 December 1997
Abstract Agrobacterium tumefaciens strain 1D1609 is reported here as the first field isolate from alfalfa (Medicago sativa L.). Unlike well-characterized A. tumefaciens strains such as C58 and Ach5, strain 1D1609 is highly virulent on alfalfa and has a distinctive host range. Interestingly, strain 1D1609 is naturally resistant to kanamycin and spectinomycin. The Ti plasmid in strain 1D1609 is an octopine-type; thus, tumors formed by strain 1D1609 synthesize octopine, which is utilized by the bacterium as a sole carbon source. Reciprocal exchange of Ti plasmids between strains 1D1609 and C58 showed that both chromosomal and Ti plasmid genes in strain 1D1609 contribute specifically to tumor formation on alfalfa. In addition, the nondormant CUF101 alfalfa cultivar from which strain 1D1609 was isolated was significantly more susceptible to all Agrobacterium strains tested than was the dormant Agate cultivar. Key words Agrobacterium tumefaciens · Alfalfa · Medicago sativa · Ti plasmid · Virulence · Octopine
improvement has depended primarily on conventional breeding techniques. Attempts to supplement the traditional methods with genetic engineering technology, such as Agrobacterium-mediated transformation (Shahin et al. 1986; Chabaud et al. 1988; D’Halluin et al. 1990; Desgagn’s et al. 1995) to introduce useful genes, have produced mixed results, and have been complicated by the tetraploid genome of alfalfa, by the poor regeneration of commercial varieties, and by the lack of Agrobacterium strains that were specifically virulent on alfalfa. We recently isolated a highly virulent strain of Agrobacterium tumefaciens from a crown gall tumor on a field-grown alfalfa plant in the Imperial Valley of Southern California. This strain, designated 1D1609, harbors an octopine-type Ti plasmid and possesses natural resistance to kanamycin and spectinomycin. When compared with the well-characterized A. tumefaciens strains Ach5 and C58, strain 1D1609 shows marked differences in host range. Interestingly, reciprocal exchange of Ti plasmids between strains 1D1609 and C58 demonstrated that the Ti plasmid and chromosomal genes are required for efficient transformation of alfalfa by strain 1D1609.
Introduction Alfalfa (Medicago sativa L.) is an important perennial forage crop for dairy and beef cattle, poultry, and other livestock animals. Most alfalfa grown in the USA is dormant during winter months, while cultivars grown in Southern California and Arizona are genetically nondormant and susceptible to cold temperatures. To date, alfalfa
J. D. Palumbo · C. I. Kado (Y) Department of Plant Pathology, University of California, Davis, CA 95616, USA e-mail: [email protected]; Tel. +1-530-752-0325; Fax +1-530-752-5674 J. D. Palumbo · D. A. Phillips Department of Agronomy and Range Science,
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