PHYLOGENETIC RELATIONSHIPS AMONG STREPTOPHYTES AS INFERRED FROM CHLOROPLAST SMALL AND LARGE SUBUNIT rRNA GENE SEQUENCES¹

Abstract

To gain insights into the phylogeny of charophytes and into their relationships with other green algae and bryophytes, we analyzed the chloroplast small and large subunit rRNA sequences of charophytes belonging to five orders (Charales, Coleochaetales, Desmidiales, Klebsormidiales, and Zygnematales), of chlorophytes from the four remaining classes of green algae, and of bryophytes representing the three classes reported in this group of land plants. We also probed the gene organization and intron content of the chloroplast rDNA operon in charophytes and bryophytes. The organization of this operon proved to be highly conserved, except in members of the Desmidiales and Zygnematales. Homologous group II introns were identified in the trnA(UGC) gene of all charophyte groups examined and in the trnI(GAU) gene of charophytes from all orders except the Desmidiales and Zygnematales. Phylogenetic analyses of concatenated rDNA sequences consistently placed the prasinophyte Mesostigma viride Lauterborn at the base of the Streptophyta and Chlorophyta, although alternative topologies positioning Mesostigma within the Streptophyta could not be rejected. A sister group relationship was unambiguously established between Chaetosphaeridium globosum (Nordstedt) Klebahn and members of the Coleochaetales. The Charales, Coleochaetales, Desmidiales, and Zygnematales were found to be monophyletic, and a sister group relationship was observed for the Desmidiales and Zygnematales. Although our analyses failed to resolve the branching order of the Coleochaetales, Charales, Desmidiales/Zygnematales, and bryophytes, they revealed that the problematic charophyte taxon Entransia fimbriata Hughes strongly clusters with Klebsormidium flaccidum (Kützing) Silva, Mattox et Blackwell to form a basal lineage relative to the other charophyte orders examined.

Green Algae and the Origins of Multicellularity in the Plant Kingdom

“…This view has been corroborated and refined using molecular phylogenetics that have begun to clarify relationships within charophyte algae and with their sister clade, the land plants (embryophytes) (Turmel et al 2002;Finet et al 2010;Wodniok et al 2011;Laurin-Lemay et al 2012;Timme et al 2012;Zhong et al 2013).…”

Phylogeny and Molecular Evolution of the Green Algae

“…First, an unexpected result in the phylogeny of Finet et al (2010) was the grouping of Chaetosphaeridium with the Zygnematophyceae. Chaetosphaeridium has typically been placed in the Coleochaetophyceae, a position that has been supported by molecular phylogenetic studies (Karol et al, 2001;Turmel et al, 2002a), and morpho-cytological characteristics, such as the presence of typical sheathed hairs and similar chloroplast structure (Delwiche et al, 2002;Hall & Delwiche, 2007). It is certainly possible that the two genera, both of which live on aquatic plants or stones in freshwater environments, do not form a monophyletic group, but they share enough distinctive properties to cast doubt on a phylogeny that separates them.…”

“…Multi-gene phylogenies show that the Klebsormidiophyceae diverged after the Mesostigmatophyceae and Chlorokybophyceae, and is sister to the clade comprising the Charophyceae, Zygnematophyceae, Coleochaetophyceae and land plants (Karol et al, 2001;Turmel et al, 2002a;Cocquyt et al, 2010b;Finet et al, 2010;Wodniok et al, 2011). This phylogenetic position is further supported by some chloroplast genomic features, like the presence of introns in two transfer RNAs which is shared between Klebsormidium and the later-diverging streptophyte lineages, and the presence of functional plastid tufA, which is shared with the early-diverging lineages Turmel et al, 2005;Turmel et al, 2007b) (Fig.…”

The chloroplast and mitochondrial genome sequences of the charophyte Chaetosphaeridium globosum : Insights into the timing of the events that restructured organelle DNAs within the green algal lineage that led to land plants

“…Considering that trans-spliced introns have been shown to evolve from cis-spliced orthologs (23,24), the gain of a cis-spliced version of the trans-spliced rps12.i1 intron must have preceded fragmentation of the intron and relocalization of the resulting intronexon pieces. Available cpDNA sequences from zygnematalean charophytes (9,12,13) including Spirogyra indicate that the latter events as well as the insertions of the trnI(gau) and trnA(ugc) introns occurred before the emergence of the Zygnematales. The four group II introns missing from Chaetosphaeridium cpDNA might have been acquired by streptophytes after the emergence of the Chaetosphaeridium lineage, or alternatively, they might Tables 4 and 5.…”

“…Of the five orders recognized in the Charophyta (5), the Charales have been shown recently to be the closest relatives of land plants (6). A third green-plant lineage, at the base of the split of the Chlorophyta and Streptophyta, is represented possibly by the green alga Mesostigma viride (7)(8)(9). This lineage remains controversial, because some phylogenetic analyses placed Mesostigma within the Streptophyta (2,6,10).…”