CLK1, A SERINE THREONINE PROTEIN KINASE-ENCODING GENE, IS INVOLVED INPATHOGENICITY OF COLLETOTRICHUM-LINDEMUTHIANUM ON COMMON BEAN/

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, produce d very few lesions on bean leaves and appeared affected in its ability to penetrate the leaf cuticle. Molecular analyses showed that the bor der sequences of the unique integration site of the disrupting pAN7-1 plasmid in the mutant exhibited homology with conserved domains of ser ine/threonine protein kinases, The corresponding wild-type sequences w ere cloned and a gene replacement vector with a mutated copy harboring a selection marker constructed, Transformation of the wild-type patho gen produced a strain with a phenotype identical to the original mutan t, Genomic and cDNA sequences indicated that the disrupted gene is a m ember 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 synthe tic media but was undetectable during the infection even when a sensit ive reverse transcriptase-polymerase chain reaction methodology was us ed, This study represents the first characterization of altered pathog enicity mutants in C. lindemuthianum produced by random mutagenesis an d demonstrates the involvement of a member of the serine/threonine kin ase gene family in the early steps of the infection process.