Roger A J, Smith M W, Doolittle R F, Doolittle W F
Department of Biochemistry, Dalhousie University, Halifax, Nova Scotia, Canada.
J Eukaryot Microbiol. 1996 Nov-Dec;43(6):475-85. doi: 10.1111/j.1550-7408.1996.tb04507.x.
The phylogenetic relationships between major slime mould groups and the identification of their unicellular relatives has been a subject of controversy for many years. Traditionally, it has been assumed that two slime mould groups, the acrasids and the dictyostelids were related by virtue of their cellular slime mould habit; a view still endorsed by at least one current classification scheme. However, a decade ago, on the basis of detailed ultrastructural resemblances it was proposed that acrasids of the family Acrasidae were not relatives of other slime moulds but instead related to a group of mostly free-living unicellular amoebae, the Schizopyrenida. The class Heterolobosea was created to contain these organisms and has since figured in many discussions of protist evolution. We sought to test the validity of Heterolobosea by characterizing homologs of the highly conserved glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) from an acrasid, Acrasis rosea; a dictyostelid, Dictyostelium discoideum; and the schizopyrenid Naegleria andersoni. Phylogenetic analysis of these and other GAPDH sequences, using maximum parsimony, neighbour-joining distance and maximum likelihood methods strongly supports the Heterolobosea hypothesis and discredits the concept of a cellular slime mould grouping. Moreover, all of our analyses place Dictyostelium discoideum as a relatively recently originating lineage, most closely related to the Metazoa, similar to other recently published phylogenies of protein-coding genes. However, GAPDH phylogenies do not show robust branching orders for most of the relationships between major groups. We propose that several of the incongruencies observed between GAPDH and other molecular phylogenies are artifacts resulting from substitutional saturation of this enzyme.
主要黏菌群体之间的系统发育关系及其单细胞亲缘物种的鉴定多年来一直是一个有争议的话题。传统上，人们认为两个黏菌群体，即集胞黏菌和盘基网柄菌，因其细胞黏菌习性而相关；这一观点至今仍被至少一种现行分类方案所认可。然而，十年前，基于详细的超微结构相似性，有人提出集胞黏菌科的集胞黏菌并非其他黏菌的亲缘物种，而是与一组大多自由生活的单细胞变形虫，即裂核变形虫目相关。异叶足纲这一分类被创建出来以包含这些生物，此后它在许多关于原生生物进化的讨论中都有出现。我们试图通过对来自集胞黏菌玫瑰集胞黏菌、盘基网柄菌和裂核变形虫安德森内格里亚的高度保守的糖酵解酶甘油醛 - 3 - 磷酸脱氢酶（GAPDH）的同源物进行特征分析，来检验异叶足纲的有效性。使用最大简约法、邻接法距离法和最大似然法对这些以及其他GAPDH序列进行系统发育分析，有力地支持了异叶足纲假说，并使细胞黏菌分组的概念失去可信度。此外，我们所有的分析都将盘基网柄菌置于一个相对近期起源的谱系中，与后生动物关系最为密切，这与其他最近发表的蛋白质编码基因系统发育研究结果相似。然而，GAPDH系统发育分析对于主要类群之间的大多数关系并没有显示出稳健的分支顺序。我们认为，在GAPDH和其他分子系统发育之间观察到的一些不一致是由于该酶的替换饱和导致的假象。
