PHYLOGENY OF THE CONJUGATING GREEN ALGAE (ZYGNEMOPHYCEAE) BASED ON rbc  L SEQUENCES

Abstract

Sequences of the gene encoding the large subunit of RUBISCO (rbcL) for 30 genera in the six currently recognized families of conjugating green algae (Desmidiaceae, Gonatozygaceae, Mesotaeniaceae, Peniaceae, and Zygnemataceae) were analyzed using maximum parsimony and maximum likelihood; bootstrap replications were performed as a measure of support for clades. Other Charophyceae sensu Mattox and Stewart and representative land plants were used as outgroups. All analyses supported the monophyly of the conjugating green algae. The Desmidiales, or placoderm desmids, constitute a monophyletic group, with moderate to strong support for the four component families of this assemblage (Closteriaceae, Desmidiaceae, Gonatozygaceae, and Peniaceae). The analyses showed that the two families of Zygnematales (Mesotaeniaceae, Zygnemataceae), which have plesiomorphic, unornamented and unsegmented cell walls, are not monophyletic. However, combined taxa of these two traditional families may constitute a monophyletic group. Partitioning the data by codon position revealed no significant differences across all positions or between partitions of positions one and two versus position three. The trees resulting from parsimony analyses using first plus second positions versus third position differed only in topology of branches with poor bootstrap support. The tree derived from third positions only was more resolved than the tree derived from first and second positions. The rbcL-based phylogeny is largely congruent with published analyses of small subunit rDNA sequences for the Zygnematales. The molecular data do not support hypotheses of monophyly for groups of extant unicellular and filamentous or colonial desmid genera exhibiting a common cell shape. A trend is evident from simple omniradiate cell shapes to taxa with lobed cell and plastid shapes, which supports the hypothesis that chloroplast shape evolved generally from simple to complex. The data imply that multicellular placoderm desmids are monophyletic. Several anomalous placements of genera were found, including the saccoderm desmid Roya in the Gonatozygaceae and the zygnematacean Entransia in the Coleochaetales. The former is strongly supported, although the latter is not, and Entransia's phylogenetic position warrants further study.

Phylogeny and classification of Zygnematophyceae (Streptophyta): current state of affairs.

“…Not surprisingly, the first assessment with the molecular tools confirmed the anticipated monophyly of the class (BhattacharYa et al 1994, Besendahl & BhattacharYa 1999, Mccourt at al. 2000, Gontcharov et al 2003.…”

“…Ultrastructural studies in the conjugates revealed cytokinesis by a phragmoplast allying them with the Charales, Coleochaete, a few other algal taxa and embryophyte plants (Fowke & Pickett-heaPs 1969a, b, Pickett-heaPs 1975, Mattox & stewart 1984, GroliG 1992. Further biochemical and molecular data has shown an advanced position of the class Zygnematophyceae among streptophyte algae but were not conclusive regarding its exact placement there because their results were affected by insufficient taxon sampling, weak resolving power of the markers used or long-branch attraction artefact (kranz & huss 1996, BhattacharYa & Medlin 1998, chaPMan et al 1998, Qiu & PalMer 1999, Mccourt et al 2000.…”

“…The first insights into the conjugates phylogeny were obtained with nuclear-encoded SSU rRNA and chloroplast protein-coding rbcL genes and these markers remain to be the major source of information in the class (BhattacharYa et al 1994, Mccourt et al 1995, 2000, Besendahl & BhattacharYa 1999, Gontcharov et al 2003, 2004. in early phylogenetic analyses these molecular markers independently confirmed monophyly of the class and the order Desmidiales but also rejected monophyly of the order Zygnematales and its two families Zygnemataceae and Mesotaeniaceae.…”

“…Conjugating green algae were always considered as a natural group, only affiliation of the genus Entransia huGhes to it was somewhat questionable (kadluBowska 1984, Mccourt et al 2000. Not surprisingly, the first assessment with the molecular tools confirmed the anticipated monophyly of the class (BhattacharYa et al 1994, Besendahl & BhattacharYa 1999, Mccourt at al.…”

Molecular and morphological diversity of Zygnema and Zygnemopsis (Zygnematophyceae, Streptophyta) from Svalbard (High Arctic)

“…(2015), but with 50 µl of Instagene Matrix instead of 100 µl (Bio-Rad Laboratories, USA). Primers RH1 and 1385R (McCourt et al ., 2000), and newly designed primers ZygF (5’TATGTCAACCACAAAC3’) and ZygR (5’GTATCAAATTCAAATTTA3’), were used for amplification of the rbc L gene in reactions containing 13.9 µl of sterile Milli-Q water, 2 µl of MgCl 2 (25 mM), 2 µl of AmpliTaq Gold 360 Buffer (Applied Biosystems, Carlsbad, California, USA), 0.4 µl of dNTP mix (10 mM), 0.25 µl of forward and reverse primer (25 pmol ml –1 ), 0.2 µl of AmpliTaq Gold 360 DNA Polymerase and 1 µl of DNA (10 ng µl –1 ). Cycling was performed with an initial denaturation for 10 min at 95°C, followed by 35 amplification cycles of 1 min denaturation at 94°C, 1 min annealing at 48°C and 2.5 min extension at 72°C, and a final extension at 72°C for 10 min.…”