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Identification of New Candidate Pathogenicity Factors in the Xylem-Invading Pathogen Xanthomonas albilineans by Transposon Mutagenesis

May 2011 , Volume 24 , Number  5
Pages  594 - 605

Philippe Rott,1,2 Laura Fleites,2 Gary Marlow,2 Monique Royer,1 and Dean W. Gabriel2

1UMR BGPI, CIRAD, TA A-54/K, Campus International de Baillarguet, 34398 Montpellier Cedex 5, France; 2Department of Plant Pathology, University of Florida, Gainesville 32605, U.S.A.

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Accepted 16 December 2010.

Xanthomonas albilineans is a xylem-invading pathogen that produces the toxin albicidin that blocks chloroplast differentiation, resulting in disease symptoms of sugarcane leaf scald. In contrast to other xanthomonads, X. albilineans does not possess a hypersensitive response and pathogenicity type III secretion system and does not produce xanthan gum. Albicidin is the only previously known pathogenicity factor in X. albilineans, yet albicidin-deficient mutant strains are still able to efficiently colonize sugarcane. To identify additional host adaptation or pathogenicity factors, sugarcane ‘CP80-1743’ was inoculated with 1,216 independently derived Tn5 insertions in X. albilineans XaFL07-1 from Florida. Sixty-one Tn5 mutants were affected in development of leaf symptoms or in stalk colonization. The Tn5 insertion sites of these mutants were determined and the interrupted genes were identified using the recently available genomic DNA sequence of X. albilineans GPE PC73 from Guadeloupe. Several pathogenicity-related loci that were not previously reported in Xanthomonas spp. were identified, including loci encoding hypothetical proteins, a membrane fusion protein conferring resistance to novobiocin, transport proteins, TonB-dependent outer-membrane transporters, and an OmpA family outer-membrane protein.

© 2011 The American Phytopathological Society