ALGAE CONTAINING CHLOROPHYLLS a + c ARE PARAPHYLETIC: MOLECULAR EVOLUTIONARY ANALYSIS OF THE CHROMOPHYTA

Abstract

Abstract. -Sequence comparisons of small subunit ribosomal RNA coding regions from 12 chlorophylls a + c-containing algae were used to infer phylogenetic relationships within the Chromophytao Three chromophyte lines of descent, delineated by the Bacillariophyceae, the Phaeophyceael Xanthophyceae, and the Chrysophyceae/Eustigmatophyceae/Synurophyceae are members of a complex evolutionary assemblage, which also includes representatives of the Oomycota ("lower" fungi). Maximum parsimony and distance matrix methods demonstrate a common evolutionary history for these lineages but their relative branching order could not be determined. Other algal species with chlorophylls a + c, including dinoflagellates and prymnesiophytes, are not members of this complex assemblage. Dinoflagellates are specifically related to apicomplexans and ciliates, and the prymnesiophyte, Emiliania huxleyi, represents an independent photosynthetic lineage that separated from other eukaryotes during the nearly simultaneous divergence of plants, animals, fungi, and a number of other protist lineages. The small subunit rRNA phylogenies of chromophytes/oomycetes were compared to those derived from comparisons of ultrastructural characters. Only tubular, tripartite mastigonemes (flagellar hairs) characterized all studied taxa of chromophytes/oomycetes as a monophyletic assemblage.Key words.-Chromophyte algae, phylogeny, rRNA.Received August 5, 1991. Accepted February 26, 1992 Eukaryotic algae are nonvascular plants that have been traditionally classified according to plastic characteristics such as accessory pigments and thylakoid structure (Dodge, 1974;Taylor, 1976). The major taxonomic groups include red algae (Rhodophyta), green algae (Chlorophyta), and brown plus golden-brown algae (Chromophyta). Ultrastructure and molecular sequence similiarities demonstrate that chlorophylls a + b containing green algae (except for photosynthetic euglenoids) share a unique evolutionary history with multicellular green plants. In contrast the Rhodophyta and Chromophyta are members of the Protista which is represented by paraphyletic lines of descent that cannot be definitively placed in a phylogenetic context using traditional methods of comparative morphology, physiology, or biochemistry. This is especially true for chromophytes since they can no longer be considered as a I Address for reprint requests. monophyletic group on the basis of plastid features (Gunderson et al., 1987;Bhattacharya and Druehl, 1988;Williams, 1991;Andersen, 1991). For example, dinoflagellates have plastids containing chlorophylls a + c and were traditionally placed within the Chromophyta (Christensen, 1980(Christensen, , 1989South and Whittick, 1987;Dodge, 1989) but molecular studies show their relationship with apicomplexans and ciliated protozoa (Gajadhar et al., 1991).The Chromophyta are traditionally defined by 10 major classes which can be differentiated on the basis ofultrastructure and plastid characteristics (Green et al., 1989). The classes include the Bacillariophyceae, Chry...

Ascomycete Systematics

“…This result is consistent with the many differences between slime molds and fungi in terms of form, function and life cycle. Similarly, 18S rDNA analysis of Oomycota shows these organisms to be part of the clade including brown algae, diatoms, and other algae containing chlorophylls a and c (Forster et al, 1990;Bhattacharya et al, 1992), again a result consistent with phenotypic characters (Barr, 1981). .…”

Photosynthetic eukaryotes unite: endosymbiosis connects the dots

“…The haptophytes and stramenopiles, however, share characters such as tubular mitochondrial cristae, similar storage products, and fucoxanthin that suggest a specific relationship between these taxa. (24) The combined plastid gene tree (Fig. 2) appears to have settled the issue of chromist monophyly by providing secondary, and C: tertiary endosymbiosis.…”

“…In this study, we addressed one cornerstone of the chromalveolate hypothesis that had not yet been adequately tested using multiple nuclear loci, the monophyly of the Chromista (see Table 1). (33) This group previously had little justification on morphological (24) or phylogenetic grounds (nuclear and mitochondrial loci do not resolve their positions) (4,11,13) for being united in a single lineage. They primarily share a four-membrane-bound chlorophyll c-containing plastid that is located within the lumen of the rough endoplasmic reticulum.…”

“…(22,23) This type of eukaryote-eukaryote endosymbiosis explains the vast majority of algal diversity. Secondary plastids are found in algae containing chlorophyll c (chromophytic algae) (24) and nongreen algal/plant forms containing chlorophyll b (euglenids and chlorarachniophytes), and are unambiguously identified by the presence of three or four bounding membranes ( Table 1). The extra membranes, from inside out, are thought to be the plasma membrane of the engulfed alga (3rd) and the phagosomal membrane of the host cell of the secondary plastid (4th).…”

Developments in the taxonomy of silica‐scaled chrysophytes – from morphological and ultrastructural to molecular approaches

“…The first DNA sequences of silica‐scaled chrysophytes were published in the early 1990s, as parts of studies investigating the general phylogeny of Stramenopiles organisms (Ariztia et al 1991, Bhattacharya et al 1992). The earliest phylogenetic study focusing on scale bearing chrysophytes was published by Lavau et al (1997), who performed a MP (maximum parsimony) analyses based on nuclear SSU rDNA data and scale characteristics of 17 species of Mallomonas, Synura , and Tessellaria .…”