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Molecular Plant Pathology

Genetic Analysis of a DNA Region Involved in Expression of Two Epitopes Associated with Lipopolysaccharide in Xanthomonas campestris pv. vesicatoria. J. B. Jones, Gulf Coast Research & Education Center, University of Florida, 5007 60th St. East, Bradenton 34203; G. V. Minsavage(2), R. E. Stall(3), R. O. Kelly(4), and H. Bouzar(5). (2)(3)Department of Plant Pathology, University of Florida, Gainesville 32611; (4)(5)Gulf Coast Research & Education Center, University of Florida, 5007 60th St. East, Bradenton 34203. Phytopathology 83:548-551. Accepted for publication 18 January 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-551.

We report on the cloning of DNA involved in expression of two epitopes associated with lipopolysaccharide (LPS) in Xanthomonas campestris pv. vesicatoria and on the use of part of this region for differentiating A (nonpectolytic/amylolytic) and B strains (pectolytic/amylolytic) of this pathogen. From a genomic library of A-strain 75-3 that expresses two epitopes, two recombinant cosmids conferred expression of two epitopes in 87-13, an A strain that does not express the two epitopes. One of the two overlapping clones, pEC795, contained a 27-kb insert and was used for further analysis. Immunoblots revealed that the epitopes are components of LPS in 75-3. Transposon mutagenesis of the insert identified a 4.5- to 5.5-kb region necessary for expression of the two epitopes in 87-13. A 0.65-kb internal fragment from this region reacted strongly in hybridization tests with A strains, weakly with B strains, and with only two of eight pathovars of X. campestris. PCR (polymerase chain reaction) amplification using primers from the 0.65-kb fragment resulted in the predicted DNA product in all A strains (12), in one of 12 B strains, and in one of 10 other pathovars (i.e., X. c. pv. alfalfae). Digestion of the PCR products by two enzymes resulted in identical restriction patterns for A strains and X. c. pv. alfalfae but resulted in a different pattern for the B strain.