Molecular Systematics of Homobasidiomycetes Emphasizing Polyporaceae and Corticiaceae

小行星9629427 同担子菌纲是一组不同的真菌，包括蘑菇，多孔菌，马勃菌，臭角菌，珊瑚真菌等。许多物种分解死亡的有机物，在营养循环中很重要。其他包括植物病原体、外生真菌（与树根共生）、地衣形成真菌以及与节肢动物（如新热带区的切叶蚁）的互利伙伴。尽管它们在生态和经济上的重要性，但同担子菌的进化或系统发育关系还没有得到很好的理解。其中一个原因是真菌在解剖学上很简单，因此它们表现出很少的特征，这些特征可以用于区分它们并推断分类关系。另一个令人困惑的因素是真菌的化石记录一般都很差，尤其是肉质的同担子菌。 哈佛大学的Michael Donoghue博士和大卫Hibbett博士的研究旨在利用DNA序列确定同担子菌之间的进化关系。被测序的基因称为rDNA，编码构成核糖体（参与蛋白质合成的细胞器）的核酸。rDNAs在序列上高度保守，这使得它们可用于推断非常古老的进化分歧。核和线粒体的rDNAs正在被测序，从同一套示范分类群。这些序列被相互比对，并使用计算机算法进行分析，该算法基于基因DNA序列中的变异模式（突变取代）来估计基因之间的关系。由此产生的进化假说被表示为系统发育树。同担子菌的两个主要类群是本研究的重点，多孔菌科（Polyporaceae）和革菌科（Corticiaceae）。多孔菌科包括具有多孔状子实体的真菌，例如许多“托架真菌”，而革菌科包括具有简单的、后仰的（光滑的、壳状的）子实体的真菌。这两个科主要是基于一些宏观形态特征，但解剖学证据表明，它们是由来自许多不同进化谱系的物种组成的。一个主要的问题正在解决的是：是形态简单的corticioid真菌的一个plesiomorphic（原始）组从其他更复杂的形式已经派生，或corticioid形式从更复杂的形式通过减少和简化进化？

9629427 Donoghue Homobasidiomycetes are a diverse group of fungi that includes mushrooms, polypores, puffballs, stinkhorns, coral fungi, and others. Many species decay dead organic matter and are important in nutrient cycling. Others include plant pathogens, ectomycorrhizae (symbiotic associates of tree roots), lichen-forming fungi, and mutualist partners with arthropods such as the leaf-cutter ants of the neotropics. Despite their ecological and economic importance, the evolutionary or phylogenetic relationships of homobasidiomycetes are not well understood. One reason for this is that fungi are anatomically simple, and hence they display few characters that could be useful for discriminating among them and inferring taxonomic relationships. Another confounding factor is the poor fossil record for fungi in general, and for fleshy homobasidiomycetes in particular. Research by Drs. Michael Donoghue and David Hibbett at Harvard University is directed toward the goal of determining evolutionary relationships among the homobasidiomycetes using DNA sequences. The genes to be sequenced, called rDNA, encode the nucleic acids that make up ribosomes (organelles involved in protein synthesis). The rDNAs are highly conserved in sequence, which makes them useful for inferring very ancient evolutionary divergences. Both nuclear and mitochondrial rDNAs are being sequenced, from the same set of exemplar taxa. The sequences are aligned to each other and analyzed using computer algorithms that estimate relationships among genes based on the pattern of variation (mutational substitutions) in their DNA sequences. The resulting evolutionary hypothesis is represented as a phylogenetic tree. Two main groups of homobasidiomycetes are the focus of this research, the Polyporaceae and the Corticiaceae. The Polyporaceae includes fungi with poroid fruiting bodies such as many "bracket fungi", whereas the Corticiaceae includes fungi that have simple, resupinate (smooth, crust-like) fruiting bodies. Both families are de limited primarily on the basis of a few macromorphological features, but anatomical evidence suggests that they are composed of species from many different evolutionary lineages. One major question being addressed is: are the morphologically simple corticioid fungi a plesiomorphic (primitive) group from which other more complex forms have been derived, or have the corticioid forms evolved by reduction and simplification from more elaborate forms?