Introduction

Late blight caused by Phytophthora infestans is a devastating disease of potato and tomato in the U.S. and worldwide. Epidemics due to P. infestans in 1845 led to the Irish potato famine and the mass migration and death of millions of people in Ireland. Late blight is now considered a re-emerging disease and has reached epidemic proportions in North America and Europe due to the development of resistance to the fungicide metalaxyl in populations of the pathogen and the widespread occurrence of new genotypes. The pathogen causes a destructive foliar blight and also infects potato tubers and tomato fruit under cool, moist conditions.

While great advances have been made in the area of human genomics, we know little about the genomes of plant pathogens. Phytophthora species are responsible for billions of dollars of losses on hundreds of different food crops worldwide. Oomycetes occur in manydiverse niches in terrestrial and aquatic habitats and are a unique group of organisms distinct from true-fungi. They are known to cause disease in plant, mammalian and insect systems. P. infestans was ranked number two by the American Phytopathological Society on the list of plant pathogen species targeted for DNA sequencing and whole genome sequencing is now underway at the Whitehead Institute at MIT. There is a large database of genetic information available on P. infestans including a genetic linkage map and expressed sequence tag (EST) libraries and genetic systems are tractable. In addition, the Phytophthora research community holds regular meetings and exchanges information freely and has formed the Phytophthora Molecular Genetic Network whose goal is to facilitate the exchange of information and resources related to Phytophthora molecular genetics.

North Carolina State University and TIGR are collaborating on sequencing and annotation of haplotypes of the mitochondrial genome P. infestans. One tool that would be of use to scientists and growers would be the ability to rapidly genotype isolates of the pathogen. Haplotypes could be correlated with virulence and resistance to pesticides and used in epidemiological studies. In addition, whole mitochondrial genome sequence analysis will be useful in studies to examine molecular evolution in the pathogen.

The mitochondrial genome of P. infestans isolate ATCC-16981 has been sequenced and annotated (Genbank Accession NC_002387). This "reference" sequence represents the Ib haplotype. In this collaborative project, we will sequence, annotate and compare the sequence of three additional isolates of P. infestans. The primary use of these data will be the identification of sequence-based polymorphisms between these haplotypes, which can be used to develop diagnostic tools, track migration patterns, and study molecular evolution in the pathogen.

Project Members