The Distribution of Elongation Factor-1 Alpha (EF-1α), Elongation Factor-Like (EFL), and a Non-Canonical Genetic Code in the Ulvophyceae: Discrete Genetic Characters Support a Consistent Phylogenetic Framework

ABSTRACT. The systematics of the green algal class Ulvophyceae have been difficult to resolve with ultrastructural and molecular phylogenetic analyses. Therefore, we investigated relationships among ulvophycean orders by determining the distribution of two discrete genetic characters previously identified only in the order Dasycladales. First, Acetabularia acetabulum uses the core translation GTPase Elongation Factor 1α (EF-1α) while most Chlorophyta instead possess the related GTPase Elongation Factor-Like (EFL). Second, the nuclear genomes of dasycladaleans A. acetabulum and Batophora oerstedii use a rare non-canonical genetic code in which the canonical termination codons TAA and TAG instead encode glutamine. Representatives of Ulvales and Ulotrichales were found to encode EFL, while Caulerpales, Dasycladales, Siphonocladales, and Ignatius tetrasporus were found to encode EF-1α, in congruence with the two major lineages previously proposed for the Ulvophyceae. The EF-1α of I. tetrasporus supports its relationship with Caulerpales/Dasycladales/Siphonocladales, in agreement with ultrastructural evidence, but contrary to certain small subunit rRNA analyses that place it with Ulvales/Ulotrichales. The same non-canonical genetic code previously described in A. acetabulum was observed in EF-1α sequences from Parvocaulis pusillus (Dasycladales), Chaetomorpha coliformis , and Cladophora cf. crinalis (Siphonocladales), whereas Caulerpales use the universal code. This supports a sister relationship between Siphonocladales and Dasycladales and further refines our understanding of ulvophycean phylogeny.     

Studies of the green alga Percursaria dawsonii (=Blidingia dawsonii comb. nov., Kornmanniaceae, Ulvales) in British Columbia

We cultured and sequenced newly collected material of Percursaria dawsonii Hollenberg et I. A. Abbott, a poorly known epibiont of limpets found along the west coast of North America. Zoospores, parthenogametes, and zygotes exhibited empty‐spore germination, which produced a prostrate system that expanded by stolon‐like development. A dense carpet of initially uniseriate filaments arose from the prostrate system. These upright filaments soon became biseriate proximally and pluriseriate distally, where they were flat, twisted and distromatic for approximately four‐fifths of their length and rarely became hollow in larger individuals. These fronds became fertile distally and released quadriflagellate zoospores and/or biflagellate isogametes. Individual gametophytic fronds were dioecious, and alternated with isomorphic sporophytic fronds. The gametes moved rapidly and often exhibited an unusual side‐to‐side vibration that made them appear like winged insects. Comparisons of 18S rRNA gene and ITS sequences indicated that P. dawsonii should be included in the genus Blidingia, family Kornmanniaceae.     

Chemical structure and antiviral activity of the sulfated heterorhamnan isolated from the green seaweed Gayralia oxysperma

A homogeneous sulfated heterorhamnan was obtained by aqueous extraction, then by ultrafiltration from the green seaweed Gayralia oxysperma. Besides α-l-rhamnose it contains glucuronic and galacturonic acids, xylose and glucose. The structure was established by methylation analyses of the carboxyl-reduced, carboxyl-reduced/desulfated, carboxyl-reduced/Smith-degraded, and carboxyl-reduced/Smith-degraded/desulfated products and 1D, 2D NMR spectroscopy analyses. The heterorhamnan backbone is constituted by 3- and 2-linked rhamnosyl units (1.00:0.80), the latter being ∼50% substituted at C-3 by side chains containing 2-sulfated glucuronic and galacturonic acids and xylosyl units. The 3- and 2-linked rhamnosyl units are unsulfated (20%), disulfated (16%), and mostly monosulfated at C-2 (27%) and C-4 (37%). The branched and sulfated heterorhamnan had high and specific activity against herpes simplex virus.     

PHYLOGENETIC POSITION OF BOLBOCOLEON PILIFERUM (ULVOPHYCEAE,CHLOROPHYTA): EVIDENCE FROM REPRODUCTION,ZOOSPORE AND GAMETE ULTRASTRUCTURE,AND SMALL SUBUNIT RRNA GENE SEQUENCES1

Aspects of the reproduction of Bolbocoleon piliferum N. Pringsheim, a common, small, filamentous, endophytic marine green alga, were examined by LM and TEM. These observations were combined with phylogenetic analysis of nuclear‐encoded small subunit rRNA gene sequences to assess the phylogenetic position of B. piliferum. Quadriflagellate zoospores and planozygotes derived from fusion of isogametes yielded plants with identical morphology. Zoosporangia and gametangia divided by sequential cleavages. Plugs at the apices of zoosporangia and gametangia formed during development; tubes were found at zoosporangial and gametangial apices after swarmer release. Flagellar apparatuses of zoospores and gametes were similar to those of algae in the Ulvales (Ulvophyceae), except that terminal caps were entire rather than bilobed and rhizoplasts and “stacked” microtubular root configurations were absent. Structures associated with planozygotes were identical to those observed in other algae currently assigned to Ulotrichales and Ulvales. Molecular phylogenetic analyses placed B. piliferum within the Ulvophyceae, at the base of a clade that contains representatives of the families Ulvaceae, Ulvellaceae, and Kornmanniaceae. The results support an earlier hypothesis that B. piliferum constitutes a distinct lineage. Analyses including Kornmanniaceae recover monophyletic Ulotrichales and Ulvales, whereas analyses omitting the Kornmanniaceae indicate that Ulotrichales is paraphyletic. The structures associated with gamete fusion are conserved within Ulotrichales and Ulvales and perhaps more widely within Chlorophyta.     

A preliminary list of sublittoral marine algae from the west of Scotland

The valves and girdle bands of Melosira varians C. A. Agardh have been shown to possess greater detail than had been supposed from light microscopy. Spines, pores and projections on the surface of the loculate valve are described, and the precise relationships of the girdle bands to each other and to the valves have been elucidated.     

饶氏藻系统位置的研究

用18S rDNA基因序列分析饶氏藻属(Jaoa)与相关藻类的亲缘关系。结果表明:饶氏藻18S rDNA的长度为1632 bp,GC%为50.6%,泡状饶氏藻18S rDNA的长度为1639 bp,GC%为50.3%。用最大简约法与饶氏藻上一级分类单元(目)构建的系统树表明有4个大的分支。两种饶氏藻与石莼目的 Ulva curvata、U.rigida、Enteromorpha intestinalis和Monostroma grevillei构成很强的支持分支(分支B),它们之间的核苷酸趋异性最低仅0.041,而与胶毛藻目的 Chaetophora incrassata的趋异性则很显著,达0.112,因此,饶氏藻应属于石莼目的一个类群,且饶氏藻和泡状饶氏藻构成一单系起源的分支,这两个物种的趋异性仅0.002,显示出它们具有非常紧密的亲缘关系,很可能是1种1变种而不是2种。     

GENE SEQUENCE DIVERSITY AND THE PHYLOGENETIC POSITION OF ALGAE ASSIGNED TO THE GENERA PHAEOPHILA AND OCHLOCHAETE (ULVOPHYCEAE,CHLOROPHYTA)1

The phylogenetic position of microfilamentous marine green algae assigned to the species Phaeophila dendroides, Entocladia tenuis (Phaeophila tenuis, and Ochlochaete hystrix was examined through phylogenetic analyses of nuclear‐encoded small subunit rDNA and chloroplast‐encoded tufA gene sequences. These analyses placed the P. dendroides strains within the Ulvophyceae, at the base of a clade that contains representatives of the families Ulvaceae, Ulvellaceae, and the species Bolbocoleon piliferum, supporting an earlier hypothesis that P. dendroides constitutes a distinct lineage. Substantial divergence in both nuclear and plastid DNA sequences exists among strains of P. dendroides from different geographic localities, but these isolated strains are morphologically indistinguishable. The lineage may have an accelerated rate of gene sequence evolution relative to other microfilamentous marine green algae. Entocladia tenuis and O. hystrix are placed neither in the P. dendroides clade nor in the Ulvellaceae as previous taxonomic schemes predicted but instead form a new clade or clades at the base of the Ulvaceae. Ruthnielsenia gen. nov. is proposed to accommodate Kylin's species, which cannot be placed in Entocladia (=Acrochaete), Phaeophila, or Ochlochaete. Ruthnielsenia tenuis (Kylin) comb. nov., previously known only from Atlantic coasts, is reported for the first time from the Pacific coast of North America (San Juan Island, WA, USA). Isolates of R. tenuis from the Atlantic and Pacific coasts of North America have identical small subunit rDNA and tufA gene sequences.