EVOLUTION OF THE FREQUENCY (FRQ) CLOCK LOCUS IN ASCOMYCETE FUNGI

The frequency (frq) locus of Neurospora crassa plays a key role in the organization of circadian rhythms. Similar timing systems have been f ound in nearly all eukaryotes as well as some prokaryotes; thus,frq ma y be an excellent gene with which to conduct evolutionary studies. To investigate, we used the cloned frq locus from ascomycete fungi repres enting two classical taxonomic classes and three orders to examine two open questions in ascomycete evolution. Class Pyrenomycetidae is repr esented by several species of Neurospora, Sordaria fimicola, and Chrom ocrea spinulosa; class Loculoascomycetidae is represented by the marin e fungus Leptosphaeria australiensis. Generation of detailed restricti on maps of homologs from the Neurospora species allows analysis of evo lutionary relationships among these closely related species. A maximum -parsimony tree based on these restriction data suggests that Neurospo ra tetrasperma groups more closely with Neurospora sitophila than with Neurospora crassa using the homothallic species Neurospora galapagose nsis as an outgroup. A maximum-parsimony tree derived using amino acid sequences from Neurospora crassa, Sordaria fimicola, Chromocrea spinu losa, and Leptosphaeria australiensis surprisingly suggests that Lepto sphaeria australiensis should be classified within Pyrenomycetes rathe r than in a separate class. This suggestion is based on the observatio ns that Leptosphaeria groups with Chromocrea on an evolutionary tree, is more closely related to Neurospora and Sordaria than is Chromocrea, and shares a conserved intron with Chromocrea. Together, these data s how that frq is a useful gene with which to conduct evolutionary studi es.