Evolution of the frequency (frq) clock locus in Ascomycete fungi.

The frequency (fr4) locus of Neurosporu crussa plays a key role in the organization of circadian rhythms. Similar timing systems have been found in nearly all eukaryotes as well as some prokaryotes; thus,frq may be an excellent gene with which to conduct evolutionary studies. To investigate, we used the cloned fj-q locus from ascomycete fungi representing two classical taxonomic classes and three orders to examine two open questions in ascomycete evolution. Class Pyrenomycetidae is represented by several species of Neurospora, Sorduria jimicola, and Chromocrea spinulosa; class Loculoascomycetidae is represented by the marine fungus Leptosphaeria austruliensis. Generation of detailed restriction maps of homologs from the Neurosporu species allows analysis of evolutionary relationships among these closely related species. A maximum-parsimony tree based on these restriction data suggests that Neurospora tetrasperma groups more closely with Neurospora sitophila than with Neurospora crassa using the homothallic species Neurosporu galupagosensis as an outgroup. A maximum-parsimony tree derived using amino acid sequences from Neurospora crassa, Sordaria jimicola, Chromocrea spinulosa, and Leptosphaeria australiensis surprisingly suggests that Leptosphaeria austruliensis should be classified within Pyrenomycetes rather than in a separate class. This suggestion is based on the observations that Leptosphaeria groups with Chromocrea on an evolutionary tree, is more closely related to Neurosporu and Sorduria than is Chromocrea, and shares a conserved in&on with Chromocrea. Together, these data show that frq is a useful gene with which to conduct evolutionary studies.