Coordination mechanism of cell and cyanelle division in the glaucophyte alga Cyanophora sudae

In unicellular algae with a single chloroplast, two mechanisms coordinate cell and chloroplast division: the S phase-specific expression of chloroplast division genes and the permission of cell cycle progression from prophase to metaphase by the onset of chloroplast division. This study investigated whether a similar mechanism exists in a unicellular alga with multiple chloroplasts using the glaucophyte alga Cyanophora sudae, which contains four chloroplasts (cyanelles). Cells with eight cyanelles appeared after the S phase arrest with a topoisomerase inhibitor camptothecin, suggesting that the mechanism of S phase-specific expression of cyanelle division genes was conserved in this alga. Inhibition of peptidoglycan synthesis by β-lactam antibiotic ampicillin arrested cells in the S-G2 phase, and inhibition of septum invagination with cephalexin resulted in cells with two nuclei and one cyanelle, despite inhibition of cyanelle division. This indicates that even in the unicellular alga with four chloroplasts, the cell cycle progresses to the M phase following the progression of chloroplast division to a certain division stage. These results suggested that C. sudae has two mechanisms for coordinating cell and cyanelle division, similar to the unicellular algae with a single chloroplast.

Gene expression analysis of Cyanophora paradoxa reveals conserved abiotic stress responses between basal algae and flowering plants

The glaucophyte Cyanophora paradoxa represents the most basal member of the kingdom Archaeplastida, but the function and expression of most of its genes are unknown. This information is needed to uncover how functional gene modules, that is groups of genes performing a given function, evolved in the plant kingdom. We have generated a gene expression atlas capturing responses of Cyanophora to various abiotic stresses. The data were included in the CoNekT-Plants database, enabling comparative transcriptomic analyses across two algae and six land plants. We demonstrate how the database can be used to study gene expression, co-expression networks and gene function in Cyanophora, and how conserved transcriptional programs can be identified. We identified gene modules involved in phycobilisome biosynthesis, response to high light and cell division. While we observed no correlation between the number of differentially expressed genes and the impact on growth of Cyanophora, we found that the response to stress involves a conserved, kingdom-wide transcriptional reprogramming, which is activated upon most stresses in algae and land plants. The Cyanophora stress gene expression atlas and the tools found in the https://conekt.plant.tools/ database thus provide a useful resource to reveal functionally related genes and stress responses in the plant kingdom.

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

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 mitochondrial genomes of the glaucophytes Gloeochaete wittrockiana and Cyanoptyche gloeocystis: multilocus phylogenetics suggests a monophyletic archaeplastida

A significant limitation when testing the putative single origin of primary plastids and the monophyly of the Archaeplastida supergroup, comprised of the red algae, viridiplants, and glaucophytes, is the scarce nuclear and organellar genome data available from the latter lineage. The Glaucophyta are a key algal group when investigating the origin and early diversification of photosynthetic eukaryotes. However, so far only the plastid and mitochondrial genomes of the glaucophytes Cyanophora paradoxa (strain CCMP 329) and Glaucocystis nostochinearum (strain UTEX 64) have been completely sequenced. Here, we present the complete mitochondrial genomes of Gloeochaete wittrockiana SAG 46.84 (36.05 kb; 33 protein-coding genes, 6 unidentified open reading frames [ORFs], and 28 transfer RNAs [tRNAs]) and Cyanoptyche gloeocystis SAG 4.97 (33.24 kb; 33 protein-coding genes, 6 unidentified ORFs, and 26 tRNAs), which represent two genera distantly related to the "well-known" Cyanophora and Glaucocystis. The mitochondrial gene repertoire of the four glaucophyte species is highly conserved, whereas the gene order shows considerable variation. Phylogenetic analyses of 14 mitochondrial genes from representative taxa from the major eukaryotic supergroups, here including novel sequences from the glaucophytes Cyanophora tetracyanea (strain NIES-764) and Cyanophora biloba (strain UTEX LB 2766), recover a clade uniting the three Archaeplastida lineages; this recovery is dependent on our novel glaucophyte data, demonstrating the importance of greater taxon sampling within the glaucophytes.