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clk1, a Serine/Threonine Protein Kinase-Encoding Gene, Is Involved in Pathogenicity of Colletotrichum lindemuthianum on Common Bean

February 1998 , Volume 11 , Number  2
Pages  99 - 108

Marie Dufresne , 1 John A. Bailey , 2 Michel Dron , 1 and Thierry Langin 1 , 3

1Laboratoire de Phytopathologie Moléculaire, Centre de Recherche sur les Plantes, ERS 569, Bâtiment 630, Université Paris-Sud, 91405 Orsay Cedex, France; 2Department of Agricultural Sciences, IACR-Long Ashton Research Station, University of Bristol, Bristol BS18 9AF, United-Kingdom; 3Laboratoire de Génétique Moléculaire des Champignons Phytopathogénes, Institut de Génétique et Microbiologie, URA, Bâtiment 400, Université Paris-Sud, 91405 Orsay Cedex, France

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Accepted 24 October 1997.

A random insertional mutagenesis in Colletotrichum lindemuthianum, the causal agent of common bean anthracnose, generated four mutants that showed altered pathogenicity when tested on intact seedlings, excised leaves, and/or excised hypocotyls. One of these mutants, H290, produced very few lesions on bean leaves and appeared affected in its ability to penetrate the leaf cuticle. Molecular analyses showed that the border sequences of the unique integration site of the disrupting pAN7-1 plasmid in the mutant exhibited homology with conserved domains of serine/threonine protein kinases. The corresponding wild-type sequences were cloned and a gene replacement vector with a mutated copy harboring a selection marker constructed. Transformation of the wild-type pathogen produced a strain with a phenotype identical to the original mutant. Genomic and cDNA sequences indicated that the disrupted gene is a member of the serine/threonine protein kinase family. The gene, called clk1 (Colletotrichum lindemuthianum kinase 1), was weakly expressed in the mycelium of the wild-type strain grown on rich and minimal synthetic media but was undetectable during the infection even when a sensitive reverse transcriptase-polymerase chain reaction methodology was used. This study represents the first characterization of altered pathogenicity mutants in C. lindemuthianum produced by random mutagenesis and demonstrates the involvement of a member of the serine/threonine kinase gene family in the early steps of the infection process.

© 1998 The American Phytopathological Society