The PYR1 gene of the plant pathogenic fungus Colletotrichum graminicola: selection by intraspecific complementation and sequence analysis.

A spontaneous uridine-requiring auxotroph of Colletotrichum graminicola was recovered by selection for resistance to 5-fluoro-orotic acid. The auxotroph lacked orotate phosphoribosyl transferase (OPRTase) and was complemented with a clone from a cosmid library of C. graminicola DNA. A 3.1 kb HindIII-SalI fragment was subcloned from the cosmid and it could efficiently transform the auxotrophic strain to uridine prototrophy and integrate by site-specific recombination. This DNA fragment contains an open reading frame that is similar to OPRTase genes of the fungi Sordaria macrospora, Trichoderma reesei, Podospora anserina, and Saccharomyces cerevisiae. Based on the sequence similarities and the ability to restore uridine prototrophy, we conclude that the fragment contains the C. graminicola gene for OPRTase, which we have named PYR1. Our results demonstrate that cloning by complementation is feasible in C. graminicola, that the gene for OPRTase from C. graminicola can be useful as a selectable marker in transformation of the fungus, and that the OPRTase gene product is similar to OPRTase from other fungi.