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Transposon Mutagenesis of Xylella fastidiosa by Electroporation of Tn5 Synaptic Complexes

¹Department of Plant Pathology, University of California-Davis, 1 Shields Avenue, Davis 95616, U.S.A.; ²Epicentre Technologies, 1202 Ann Street, Madison 53713, WI, U.S.A; ³Department of Viticulture and Enology, University of California-Davis, 1 Shields Avenue, Davis 95616, U.S.A.

Pierce's disease, a lethal disease of grapevine, is caused by Xylella fastidiosa, a gram-negative, xylem-limited bacterium that is transmitted from plant to plant by xylem-feeding insects. Strains of X. fastidiosa also have been associated with diseases that cause tremendous losses in many other economically important plants, including citrus. Although the complete genome sequence of X. fastidiosa has recently been determined, the inability to transform or produce transposon mutants of X. fastidiosa has been a major impediment to understanding pathogen-, plant-, and insect-vector interactions. We evaluated the ability of four different suicide vectors carrying either Tn5 or Tn10 transposons as well as a preformed Tn5 transposase-transposon synaptic complex (transposome) to transpose X. fastidiosa. The four suicide vectors failed to produce any detectable transposition events. Electroporation of transposomes, however, yielded 6 × 10³ and 4 × 10³ Tn5 mutants per μg of DNA in two different grapevine strains of X. fastidiosa. Molecular analysis showed that the transposition insertions were single, independent, stable events. Sequence analysis of the Tn5 insertion sites indicated that the transpositions occur randomly in the X. fastidiosa genome. Transposome-mediated mutagenesis should facilitate the identification of X. fastidiosa genes that mediate plant pathogenicity and insect transmission.