INCREASED EXPRESSION OF THE CALMODULIN GENE OF THE LATE BLIGHT FUNGUSPHYTOPHTHORA-INFESTANS DURING PATHOGENESIS ON POTATO

In order to isolate in planta-induced genes encoding putative pathogen icity factors of the late blight fungus Phytophthora infestans, a geno mic library was differentially screened. For the differential hybridiz ation, labeled first-strand cDNA synthesized on mRNA isolated from P. infestans-infected potato leaves and on mRNA isolated from the fungus grown in vitro were used as probes. This screening resulted in the iso lation of the P. infestans calmodulin gene. The gene, designated calA, contains an open reading frame of 447 base pairs without introns and is unique in the P. infestans genome. The predicted amino acid sequenc e is 89.9-94.6% identical to calmodulins from higher eukaryotes, where as the identity to calmodulins of higher fungi is significantly less ( 60.8-85.1%). Expression studies revealed that the P. infestans calA ge ne is constitutively expressed in in vitro grown mycelium. However, du ring pathogenesis on potato the level of P. infestans calmodulin mRNA is increased approximately fivefold.