Abstract Detail

Systematics Section / ASPT

Kim, Eunsoo [1], Wilcox, Lee [1], Graham, Linda E. [1].

Application of Bayesian analysis of ribosomal and tubulin gene sequences to unresolved issues in the origin of green plants: Phylogenetic relationships of Mesostigma viride and Apusomonas proboscidea.

Several aspects of early evolution of green algae and land plants (collectively termed Viridiplantae) are unresolved. Whether the green flagellate Mesostigma is a basal member of the Viridiplantae or the streptophytes (charophycean green algae + land plants) has not been clearly established. Further, the prevailing concept that Plantae (the primary plastid-containing groups Viridiplantae + red algae + glaucophytes) is a monophyletic group has been challenged. Additionally, the extant plastid-less protist most closely related to the ancestry of Plantae, Viridiplantae, or streptophytes has not been identified. The present Bayesian analysis of nuclear encoded alpha- and beta-tubulin and small subunit rDNA sequences was designed to clarify these issues. Our results strongly suport previous inference (based on nuclear genes) that Mesostigma viride branches with the streptophytes. This contrasts with concepts based on plastid gene sequences of Mesostigma as an early divergent member of Viridiplantae. Our analysis strongly rejected monophyly of Plantae at the p<<0.01 level, suggesting instead that Viridiplantae, red algae, and glaucophytes may well have acquired primary plastids independently. Because Apusomonas proboscidea is bikont, bactivorous, and contains a multilayered structure similar to those of streptophytes, we explored the possibility that this plastid-less protist might be related to the ancestry of plants. Our analysis revealed a sister relationship between Apusomonas and opisthokonts, but also suggested that if the eukaryotic root lies between them, Apusomonas might be an early divergent member of the lineage that includes all other bikonts and amoebozoa.

1 - University of Wisconsin-Madison, Botany, 430 Lincoln Drive, Madison, Wisconsin, 53706-1381, USA

Keywords:
Apusomonas
glaucophytes
Mesostigma
Plantae
red algae
streptophytes
Viridiplantae.

Presentation Type: Paper
Session: 2-2
Location: Cottonwood A (Snowbird Center)
Date: Monday, August 2nd, 2004
Time: 8:15 AM
Abstract ID:705