The Glaucophyta: the blue-green plants in a nutshell

Abstract

The Glaucophyta is one of the three major lineages of photosynthetic eukaryotes, together with viridiplants and red algae, united in the presumed monophyletic supergroup Archaeplastida. Glaucophytes constitute a key algal lineage to investigate both the origin of primary plastids and the evolution of algae and plants. Glaucophyte plastids possess exceptional characteristics retained from their cyanobacterial ancestor: phycobilisome antennas, a vestigial peptidoglycan wall, and carboxysome-like bodies. These latter two traits are unique among the Archaeplastida and have been suggested as evidence that the glaucophytes diverged earliest during the diversification of this supergroup. Our knowledge of glaucophytes is limited compared to viridiplants and red algae, and this has restricted our capacity to untangle the early evolution of the Archaeplastida. However, in recent years novel genomic and functional data are increasing our understanding of glaucophyte biology. Diverse comparative studies using information from the nuclear genome of <em>Cyanophora paradoxa</em> and recent transcriptomic data from other glaucophyte species provide support for the common origin of Archaeplastida. Molecular and ultrastructural studies have revealed previously unrecognized diversity in the genera <em>Cyanophora</em> and <em>Glaucocystis</em>. Overall, a series of recent findings are modifying our perspective of glaucophyte diversity and providing fresh approaches to investigate the basic biology of this rare algal group in detail.

Common ancestry of heterodimerizing TALE homeobox transcription factors across Metazoa and Archaeplastida

“…2) Rhodophyta (red algae) include diverse unicellular and multicellular organisms that diverge into four major lineages [26] (S1 Spreadsheet). 3) Glaucophyta members include only four cultured genera and possess plastids that carry ancestral features of the cyanobacterial symbiont that gave rise to photosynthetic organelles in eukaryotes [27].…”

All Eukaryotes Are Sexual, unless Proven Otherwise

“…According to Adl et al [62] Archaeplastida is composed of three major lineages, two fully sexual and one with unknown sexual activities: Rhodophyceae, Chloroplastida, and Glaucophyta, the last one with complete life cycles missing for all species. [63,64] Despite the poor molecular data available for Glaucophyta, most meiotic proteins may be detected for representatives of this group (Figure 2). Combined evidence, i.e., the close relationship with fully sexual groups, the presence of flagellated cells, and the presence of an almost complete set of meiotic proteins supports the existence of sexual cycles in glaucophytes.…”

The monoplastidic bottleneck in algae and plant evolution

“…1A). Although only 15 glaucophyte species have been described (Guiry, 2012), it is likely that more species exist (Jackson et al, 2015;Takahashi et al, 2016). The most basal-branching glaucophyte genus is Cyanophora (Chong et al, 2014).…”

“…Cyanophora cells tend to harbour either one or two plastids (in glaucophytes these are referred to as muroplasts; see Glossary in Box 1); if two are present, then they are semi-connected as if frozen in the act of division (Jackson et al, 2015;Box 2). Other glaucophyte genera, such as Cyanoptyche, Gloeochaete and Glaucocystis are polyplastidic (Jackson et al, 2015), but the muroplast morphology in Glaucocystis warrants attention as it has two stellate muroplast clusters within the cell (Schnepf et al, 1966). These clusters consist of individual muroplast lobes that at one end are held together through unknown mechanisms (Schnepf et al, 1966).…”

“…1B). The Glaucophyta are exclusively unicellular (Jackson et al, 2015). The deepest branching Rhodophyta, the Cyandiales (Yoon et al, 2006), are unicellular, too.…”