Identification of the <i>chaA</i> and <i>fwA</i> Spore Color Genes of <i>Aspergillus nidulans</i>

Wild-type <i>Aspergillus nidulans</i> asexual spores (conidia) are green due to a pigment that protects the spores against ultraviolet light. The pigment is produced by a biosynthetic pathway, the genes of which are dispersed in the genome. The backbone molecule of the pigment is a polyketide synthesized by a polyketide synthase encoded by the <i>wA</i> gene. If <i>wA</i> is not functional, the conidia are white. The polyketide is modified by a laccase encoded by the <i>yA</i> gene and inactivation of <i>yA</i> in an otherwise wild-type background results in yellow spores. Additional spore color mutations have been isolated and mapped to a locus genetically, but the genes that correspond to these loci have not been determined. Spore color markers have been useful historically, and they remain valuable in the molecular genetics era. One can determine if a transforming fragment has been successfully integrated at the <i>wA</i> or <i>yA</i> locus by simply looking at the color of transformant conidia. The genes of the potentially useful color loci <i>chaA</i> (chartreuse conidia) and <i>fwA</i> (fawn conidia) have not been identified previously. We chose a set of candidate genes for each locus by comparing the assembled genome with the genetic map. By systematically deleting these candidate genes, we identified a cytochrome P450 gene (AN10028) corresponding to <i>chaA</i>. Deletions of this gene result in chartreuse conidia and chartreuse mutations can be complemented in trans by a functional copy of this gene. With <i>fwA</i>, we found that the existing fawn mutation, <i>fwA1</i>, is a deletion of 2241 base pairs that inactivates three genes. By deleting each of these genes, we determined that <i>fwA</i> is AN1088, an EthD domain protein. Deletion of AN1088 results in fawn conidia as expected. Neither deletion of <i>chaA</i> nor <i>fwA</i> restricts growth and both should be valuable target loci for transformations. Combinations of deletions have allowed us to investigate the epistasis relationships of <i>wA</i>, <i>yA</i>, <i>chaA</i> and <i>fwA</i>.