An ammonium transporter gene is a potential pathogenicity gene in Ophiostoma novo-ulmi

The ascomycete Ophiostoma novo-ulmi is responsible for the current pandemic of Dutch elm disease. The mechanisms by which this fungus kills elmsremain unknown. The objective of this project was thus to find and characterize pathogenicity genes of O. novo-ulmi. Chromosome walking from locus Pat1 allowed us to identify candidate genes, particularly a gene sharing high sequence similarity with the Mep/Amt gene family of ammonium transporters. Comparative analysis of the highly aggressive O. novo-ulmi and the less aggressive O. ulmi showed that the two species carried different alleles for this gene and had significantly different growth rates on medium without ammonium. We are currently assessing whether the Ophiostoma ammonium transporter gene can fully restore the pseudohyphal growth defect of a Saccharomyces cerevisiae mep mutant. We are also verifying if the insertion of the O. novo-ulmi allele in a wild-type O. ulmi strain confers growth, morphological and pathogenic characteristics of O. novo-ulmi. The significance of these results will be discussed.