cyanelle

Cyanelle, commonly referred to as a cyanelle, is the plastid found in glaucophyte algae (division Glaucophyta). These organelles are believed to originate from a cyanobacterial endosymbiont and retain several ancestral features of cyanobacteria, including a peptidoglycan layer between two membranes. The cyanelle carries out photosynthesis and, like other plastids, expresses genes and synthesizes proteins essential for its function, although many genes have been transferred to the host nucleus over evolutionary time.

structurally, cyaneilles contain chlorophyll a and often phycobiliproteins, which give glaucophytes a characteristic blue-green color. They possess a double surrounding envelope and a residual peptidoglycan layer that is not found in most other plastids. The cyanelle genome is a reduced cyanobacterial-derived genome, with some genes retained for transcription and translation, while others have been relocated to the host’s nuclear genome. The organelle generally divides in coordination with the cell, reflecting its bacterial ancestry.

Evolutionarily, cyanelles are of particular interest because they provide a glimpse into the early stages of plastid evolution in plants and algae. Glaucophytes, which harbor these organelles, are considered an early-branching lineage within Archaeplastida, and the cyanelle’s retained ancestral features support models of plastid origin from a cyanobacterial endosymbiont.

Ecology and distribution, glaucophyte algae are small and predominantly found in freshwater environments, including ponds, streams, and moist soils. They can be unicellular or form simple colonies, and they play a role in primary production in their habitats. The cyanelle remains a defining feature of glaucophyte biology and a key example in studies of endosymbiosis.