Analysis of a nonribosomal peptide synthetase gene from Alternaria brassicae and flanking genomic sequences.

Very little information is currently available concerning the pathogenic determinants produced by Alternaria brassicae, the causal agent of the blackspot disease of crucifers. We screened a genomic library of this fungus and identified a nonribosomal peptide synthetase (NRPS) gene named AbrePsy1. The complete coding sequence is 22 kbp long and encodes a large protein (792 kDa) showing typical NRPS modular organization. Structural analysis of AbrePsy1 revealed four complete elongation modules, two of which have epimerization domains. In the vicinity of AbrePsy1, a second gene (named AbreAtr1), which encodes an ATP-binding cassette transporter was identified. Increased expression of AbrePsy1 and AbreAtr1 was observed during host-plant infection. However, while physically linked, these two genes are probably not functionally clustered, as their expression patterns differed.