Five Cyanophora (Cyanophorales, Glaucophyta) species delineated based on morphological and molecular data

Abstract

Cyanophora is an important glaucophyte genus of unicellular biflagellates that may have retained ancestral features of photosynthetic eukaryotes. The nuclear genome of Cyanophora was recently sequenced, but taxonomic studies of more than two strains are lacking for this genus. Furthermore, no study has used molecular methods to taxonomically delineate Cyanophora species. Here, we delimited the species of Cyanophora using light and electron microscopy, combined with molecular data from several globally distributed strains, including one newly established. Using a light microscope, we identified two distinct morphological groups: one with ovoid to ellipsoidal vegetative cells and another with dorsoventrally flattened or broad, bean-shaped vegetative cells containing duplicated plastids. Our light and scanning electron microscopy clearly distinguished three species with ovoid to ellipsoidal cells (C. paradoxa Korshikov, C. cuspidata Tos.Takah. & Nozaki sp. nov., and C. kugrensii Tos.Takah. & Nozaki sp. nov.) and two species with broad, bean-shaped cells (C. biloba Kugrens, B.L.Clay, C.J.Mey. & R.E.Lee and C. sudae Tos.Takah. & Nozaki sp. nov.) based on differences in cell shape and surface ornamentations of the vegetative cells under the field-emission scanning electron microscope. Molecular phylogenetic analyses of P700 chl a apoprotein A2 (psaB) genes and internal transcribed spacer (ITS) regions of nuclear ribosomal DNA (rDNA), as well as a comparison of secondary structures of nuclear rDNA ITS-2 and genetic distances of psaB genes, supported the delineation of five morphological species of Cyanophora.

The Glaucophyta: the blue-green plants in a nutshell

“…The delimitation of the genera Glaucocystis, Cyanoptyche, Gloeochaete, and Cyanophora were confirmed in recent molecular analyses [38,39]. Here we describe characteristics of each genus based on morphological observations of representative species available in current microbial collections.…”

“…One-to-two plastids (Fig. 3e) or a multiple of two are present in each cell [39]. Plastids often have a slight invagination at mid-periphery sometimes interpreted as evidence of organelle division [39].…”

“…The appearance of being in, or arrested in division is possibly a stable morphology. Morphological features explored in the recent delimitation of five species of Cyanophora included cell shape, flatness (dorsal/ventral), ventral groove, flagellar origin, plastid division, and ridged fenestrations (see the "Species diversity in glaucophytes" section below) [39]. Flagellar insertion (invariant) and fenestrations (overlapping) were not informative at the species level in Cyanophora but would be interesting characters to compare among genera of glaucophytes.…”

“…Recent phylogenetic analyses of the largest glaucophyte taxonomic sample to date, based on plastid (psbA and rbcL), mitochondrial (cob and cox1) and nuclear (ribosomal RNAs and the internal transcribed spacer region, ITS) markers, have revealed evidence of cryptic species diversity in the genera Cyanophora and Glaucocystis [38,39]. Phylogenetic analyses of concatenated markers from diverse genomic compartments (psbA, cob, 5S and 18S rRNAs) revealed considerable genetic divergence between different strains (NIES-763, SAG 29.80, SAG 45.84) originally recognized as Cyanophora paradoxa (Fig.…”

“…A major restriction when testing current working hypotheses regarding the evolution of the Archaeplastida has been the relative scarcity of information from Glaucophyta [16,30]. The vast majority of research efforts on glaucophytes have focused on Cyanophora paradoxa, but recent comparative genomic [8,10,37], molecular phylogenetic [38,39], proteomic [40,41], biochemical [42] and cell biology [43][44][45][46] studies have provided novel insights into the biology of this algal group. Our aim here is to provide an overview of the current knowledge of glaucophytes.…”