Isolation of putative pathogenicity genes of the potato late blight fungus Phytophthora infestans by differential hybridization of a genomic library

Abstract

Plant pathogens produce pathogenicity factors which enable them to parasitize and colonize their host. A strategy for identifying pathogenicity factors involves the isolation and characterization of genes encoding these factors. Potential pathogenicity genes are genes whose expression is induced during pathogenesis. In order to isolate such genes of the late blight Fungus Phytophthora infestans , a genomic library of P. infestans DNA was differentially hybridized using labelled first strand cDNA probes synthesized on mRNA isolated from P. infestans infected potato leaves and on mRNA isolated from the fungus grown on a basic medium in culture. In total, nine distinct in planta induced (ipi) genes were selected. Expression studies revealed that the mRNA levels of seven of these genes, ipiA, ipi C, ipiD, ipiJ1, ipiJ2, ipiN and ipi Q increased 5-10 fold during colonization. The two other genes, ipi B and ipiO, showed a transient expression pattern with the highest mRNA levels in the early stages of infection.