A gene encoding the iron-sulphur protein (Ip) subunit of succinate dehydrogenase (Sdh, EC 1.3.99.1) from Mycosphaerella graminicola (Septoria tritici) has been cloned andsequenced. The deduced amino-acid sequence exhibited a high degree of homology to Ip subunits of Sdh from other organisms; three cysteine-rich clusters associated with the iron-sulphur centres involved in electron transport were particularly conserved. Expression studies using a synthetic green fluorescent protein (SGFP) expression vector demonstrated that the cloned DNA also contained a functional promoter region and confirmed that the deduced initiation codon could act as a translational start site. Mutants resistant to the fungicide carboxin (Cbx), a known inhibitor of Sdh, were found to contain a single amino-acid substitution in the third cysteine-rich domain of the Ip protein. These mutations resulted in the conversion of a highly conserved His residue, located in a region of the protein associated with the [3Fe-4 S] high-potential non-heme iron sulphur-redox (S3) centre, to either Tyr or Leu. AnIp gene containing the His -> Tyr mutation was constructed and shown to confer Cbx resistance following co-transformation into the Cbx-sensitive wild-type strain. This confirmed that the mutation identified by sequence analysis was responsible for determining Cbx resistance.

Genomic resources available to researchers studying phytopathogenic fungi are limited. Here, we briefly review the genomic and bioinformatic resources available and the current status of fungal genomics. We also describe a relational database containing sequences of expressed sequence tags (ESTs) from three phytopathogenic fungi, Blumeria graminis, Magnaporthe grisea, and Mycosphaerella graminicola, and the methods and underlying principles required for its construction. The database contains significant annotation for each EST sequence and is accessible at http://cogeme.ex.ac.uk. An easy-to-use interface allows the user to identify gene sequences by using simple text queries or homology searches. New querying functions and large sequence sets from a variety of phytopathogenic species will be incorporated in due course.

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SUMMARY Pathogenic microbes must successfully adapt to the host environment, acquiring nutrients and tolerating immune/defence responses. Studies on host-pathogen interactions at the transcriptome level have predominantly investigated host responses. Here we present a broad-scale transcriptional analysis on a fungal pathogen during sporulation within its host environment. Septoria leaf blotch is an important fungal disease of cultivated wheat and is caused by the ascomycete fungus Septoria tritici (teleomorph Mycosphaerella graminicola). A cDNA microarray containing 2563 unigenes was generated and then used to compare fungal nutrition and development in vitro under nutrient-rich and nutrient-limiting conditions and in vivo at a late stage of plant infection. The data obtained provided clear insights into metabolic adaptation in all three conditions and an elevated stress adaptation/tolerance specifically in the host environment. We conclude that asexual sporulation of M. graminicola during the late stage of plant infection occurs in a rich nutritional environment involving adaptation to stresses imposed in part by the presence of reactive oxygen species.