Nitrate reductase of the ascomycetous fungus, Leptosphaeria maculans: gene sequence and chromosomal location.

The nitrate reductase (niaD) gene was isolated from the phytopathogenic loculoascomycete Leptosphaeria maculans by screening a genomic DNA library with the Aspergillus nidulans niaD gene. The L. maculans niaD gene is the first protein-encoding gene characterised from this fungus. It encodes a predicted protein of 893 amino acids and contains four putative introns at positions in the gene equivalent to those of four of the six introns in the A. nidulans niaD gene. Mutants defective in niaD and molybdenum cofactor gene(s) of L. maculans have been isolated. Transformation of a L. maculans niaD mutant with a 3.8 kb SacII fragment containing the L. maculans niaD gene restored wild-type growth on nitrate as a sole nitrogen source. The niaD gene is present as a single copy on a chromosome which ranges in size from 2.6 to 2.8 Mb between the different L. maculans isolates examined.