Liu Yajuan J, Hall Benjamin D
Departments of Biology and Genome Sciences, Box 355325, University of Washington, Seattle, WA 98195, USA.
Proc Natl Acad Sci U S A. 2004 Mar 30;101(13):4507-12. doi: 10.1073/pnas.0400938101. Epub 2004 Mar 19.
The mode of evolution of the biologically diverse forms of ascomycetes is not well understood, largely because the descent relationships remain unresolved. By using sequences of the nuclear gene RPB2, we have inferred with considerable resolution the phylogenetic relationships between major groups within the phylum Ascomycota. These relationships allow us to deduce a historical pattern of body plan evolution. Within Taphrinomycotina, the most basal group, two simple body plans exist: uncovered asci with unicellular growth, or rudimentary ascoma with hyphal growth. Ancestral ascomycetes were filamentous; hyphal growth was lost independently in the yeast forms of Taphrinomycotina and Saccharomycotina. Pezizomycotina, the sister group to Saccharomycotina, retained mycelial growth while elaborating two basic ontogenetic pathways for ascoma formation and centrum development. The RPB2 phylogeny shows with significant statistical support that taxa in Pezizomycotina with ascohymenial ontogeny (ascoma generally forms after nuclear pairing) are ancestral and paraphyletic, whereas ascolocular fungi with fissitunicate asci are a clade derived from them. Ascolocular lichens are polyphyletic, whereas ascohymenial lichens comprise a monophyletic group that includes the Lecanorales. Our data are not consistent with a derived origin of Eurotiomycetes including Aspergillus and Trichophyton from within a lichen-forming ancestral group. For these reasons, the results of this study are considerably at variance with the conclusion that major fungal lineages are derived from lichensymbiotic ancestors. Interpretation of our results in the context of early work suggests that ascoma ontogeny and centrum characters are not in conflict with the molecular data.
子囊菌门生物多样形式的进化模式尚未得到很好的理解，主要是因为其谱系关系仍未解决。通过使用核基因RPB2的序列，我们已经相当精确地推断出子囊菌门内主要类群之间的系统发育关系。这些关系使我们能够推断出身体结构进化的历史模式。在最基部的类群茶渍菌纲中，存在两种简单的身体结构：具单细胞生长的裸露子囊，或具菌丝生长的原始子囊果。子囊菌的祖先为丝状；菌丝生长在茶渍菌纲和酵母亚门的酵母形式中独立丧失。盘菌亚门是酵母亚门的姐妹类群，在发展出两种基本的子囊果形成和子实层发育个体发育途径的同时保留了菌丝生长。RPB2系统发育显示，具有子囊层发育（子囊果通常在核配对后形成）的盘菌亚门类群在统计学上得到显著支持，是祖先类群且并系，而具裂殖子囊的腔菌纲真菌是从它们衍生而来的一个分支。腔菌地衣是多系的，而子囊层地衣构成一个单系类群，包括茶渍目。我们的数据与包括曲霉属和毛癣菌属在内的散囊菌纲起源于地衣形成祖先类群内部的观点不一致。基于这些原因，本研究结果与主要真菌谱系起源于地衣共生祖先的结论有很大差异。在早期研究的背景下对我们的结果进行解释表明，子囊果个体发育和子实层特征与分子数据并不冲突。
