基于28S rDNA序列的鞘藻目系统发育研究

PHYLOGENETIC STUDIES OF OEDOGONIALES(CHLOROPHYCEAE,CHLOROPHYTA) BASED ON 28S rDNA SEQUENCES

作者进行了较广泛的样品采集,通过实验分离纯化培养得到多个鞘藻目种类的株系,并采用PCR技术新获得鞘藻目2属8个种类的部分28S rDNA序列,连同GenBank中的另两条序列,分析的物种涵盖了鞘藻目中的每个属。通过比较分析绿藻纲中包括此10条序列的共36个种类的同一基因序列,并选取Trebouxiophyceae中的椭圆小球藻(Chlorella ellipsoidea)和Fusochloris perforata作外类群,运用多种方法构建分子系统树,包括邻接法(Neighbor-Joining)、最大简约法(Maximum Parsimony)和Bayesian方法。3种方法所得的结果非常相似,在形态上就在整个绿藻中界限分明的鞘藻目从分子水平上再次证明为单系起源的类群;构建的系统发育树还在一定程度上表明毛鞘藻属处于鞘藻目内三个属中较分离的位置,而枝鞘藻属与鞘藻属植物并无明显界限。

The Oedogoniales is a very unusual order of green algae, and the studies about them were mainly focused on their morphological characters. But the relationship between the Oedogoniales and other greens is still hard to guarantee in terms of morphology. During the past few years various phycologists used different characteristics as basis for classification of the genera of Oedogoniales, and the relationship of the three genera was uncertain. In order to clarify the systematics problem existing in this unusual group of Oedogoniales, we collected the samples in a large area, isolated them from field and cultivated them at 20 to 25℃ at a 16 ： 8-h light： dark cycle under 25μmol photons/m^2·s, in modified of Bold＇ s Basal medium. Algal cultures were harvested by centrifugation at 7400 rpm for 2min and DNA was extracted by CTAB method. The 28S rDNA was newly amplified and sequenced from 8 species representing 2 genera （Oedocladium and Oedogonium） of Oedogoniales. Aligning with another two sequences of this order from GenBank, we succeeded to analyze the sequences covering with all the three genera of the Oedogoniales. Selecting Chlorella ellipsoidea and Fusochloris perforata as outgroups, we constructed a matrix of 38 DNA sequences. The phylogenetic trees were constructed by using Neighbor-Joining, Maximum Parsimony and Bayesian. All the three trees displayed the similar topologic structures. The results showed that the Oedogoniales was monophyletic, and within this order, the genus Oedocladium was mixed in the member of the genus Oedogonium ; whereas the genus Bulbochaete was in a divergence position to the other two genera.