Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2008
Publication Date: 10/1/2008
Citation: Bluhm, B., Dunkle, L.D. 2008. Phl1 of Cercospora zeae-maydis encodes a member of the photolyase/cryptochrome family involved in UV protection and fungal development. Fungal Genetics and Biology. 45:1364-1372. Interpretive Summary: Fungi have developed highly effective strategies to cope with harmful environmental conditions, including excessive exposure to ultraviolet irradiation. UV-induced damage to chromosomal DNA is repaired by photoylases, specialized enzymes that bind specifically to damaged DNA. Genes predicted to encode photolyases and closely related genes encoding blue-light receptors known as cryptochromes have been identified in the genomes of several filamentous fungi, but none of those has been characterized. Thus, it is unclear whether these genes function as DNA-repair enzymes or photoreceptors in fungi. The focus of this study was to identify and characterize a photolyase-like gene in the fungal pathogen Cercospora zeae-maydis, which causes gray leaf spot of maize. We cloned and disrupted PHL1, a gene highly homologous to photolyase- and cryptochrome-encoding genes from plants and animals. Disruption of PHL1 completely abolished the ability of the disruption mutants to recover from UV damage (photoreactivation), suggesting that the gene regulates components of the repair mechanism, and caused abnormalities in development and secondary metabolism. We hypothesize that fungal members of the cryptochrome/photolyase family such as PHL1 have evolved regulatory functions that distinguish them from photolyases in higher plants and animals. This study presents the first characterization of a cryptochrome/photolyase gene in a filamentous fungus and provides evidence for possible regulatory functions of these genes in fungal development. Such information will be useful to plant pathologists interested in targeting novel genes for innovative methods of disease control.
Technical Abstract: DNA photolyases harvest light energy to repair genomic lesions induced by UV light, whereas cryptochromes, paralogs of 6-4 DNA photolyases, have evolved in plants and animals as blue-light photoreceptors that function exclusively in signal transduction. Although members of the cryptochrome/photolyase family are predicted to exist in the genomes of some filamentous fungi, their function is unknown. In this study, we cloned and characterized PHL1, a cryptochrome/photolyase-like gene in the maize foliar pathogen Cercospora zeae-maydis. PHL1 was dispensable for pathogenesis, but strains disrupted in PHL1 ('phl1) showed subtle developmental abnormalities in development and secondary metabolism. Conidia of 'phl1 mutants were abolished in photoreactivation after exposure to lethal doses of UV irradiation, thus demonstrating a role for PHL1 in protection against UV light. This study presents the first characterization of a cryptochrome/photolyase gene in a filamentous fungus and provides evidence for possible regulatory functions of these genes in fungal development.