Prieto Alicia, Leal J Antonio, Bernabé Manuel, Hawksworth David L
Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Ramiro de Maeztu 9, ES-28040 Madrid, Spain.
Mycol Res. 2008 Mar;112(Pt 3):381-8. doi: 10.1016/j.mycres.2007.10.013. Epub 2007 Nov 7.
The lichen-forming order Lichinales, generally characterized by prototunicate asci and the development of thalli with cyanobacteria, has recently been recognized as a separate class of ascomycetes, Lichinomycetes, as a result of molecular phylogenetic studies. As alkali and water-soluble (F1SS) polysaccharides reflect phylogeny in other ascomycetes, a polysaccharide from Lichina pygmaea and L. confinis was purified and characterized to investigate whether these F1SS compounds in the Lichinomycetes were distinctive. Nuclear magnetic resonance (NMR) spectroscopy and chemical analyses revealed this as a galactomannan comprising a repeating unit consisting of an alpha-(1-->6)-mannan backbone, mainly substituted by single alpha-galactofuranose residues at the O-2- or the O-2,4- positions linked to a small mannan core. With the exception of the trisubstituted mannopyranose residues previously described in polysaccharides from other lichens belonging to orders now placed in Lecanoromycetes, the structure of this galactomannan most closely resembles those found in several members of the Onygenales in Eurotiomycetes. Our polysaccharide data support molecular studies showing that Lichina species are remote from Lecanoromycetes as the galactofuranose residues are in the alpha-configuration. That the Lichinomycetes were part of an ancestral lichenized group can not be established from the present data because the extracted polysaccharide does not have the galactofuranose residue in the beta configuration; however, the data does suggest that an ancestor of the Lichinomycetes contained a mannan and was part of an early radiation in the ascomycetes.
地衣形成目地卷目，通常以原壁子囊和与蓝细菌共生形成的叶状体为特征，最近由于分子系统发育研究，已被确认为子囊菌门的一个独立纲，即地卷菌纲。由于碱性和水溶性（F1SS）多糖反映了其他子囊菌的系统发育，因此对矮小地卷和相近地卷中的一种多糖进行了纯化和表征，以研究地卷菌纲中的这些F1SS化合物是否具有独特性。核磁共振（NMR）光谱和化学分析表明，这种多糖是一种半乳甘露聚糖，其重复单元由α-(1→6)-甘露聚糖主链组成，主要在与一个小甘露聚糖核心相连的O-2-或O-2,4-位置被单个α-半乳呋喃糖残基取代。除了先前在现归属于茶渍菌纲的其他地衣多糖中描述的三取代甘露吡喃糖残基外，这种半乳甘露聚糖的结构与散囊菌纲中几个发癣菌目的成员最为相似。我们的多糖数据支持分子研究结果，即地卷属物种与茶渍菌纲关系较远，因为半乳呋喃糖残基为α构型。仅根据目前的数据无法确定地卷菌纲是原始地衣化类群的一部分，因为提取的多糖不具有β构型的半乳呋喃糖残基；然而，数据确实表明地卷菌纲的一个祖先含有甘露聚糖，并且是子囊菌早期辐射的一部分。
