plastidlike

Plastidlike is a term used in cell biology to describe organelles, compartments, or structures that resemble plastids in their origin, architecture, or functional role, but are not conventional photosynthetic plastids found in plants and green algae. The concept covers reduced or secondary plastids and other endosymbiont-derived compartments that persist in diverse eukaryotic lineages. Plastidlike organelles are typically bounded by multiple membranes and often harbor plastid-type metabolic pathways, even when they do not perform photosynthesis. They may contain reduced genomes or rely on a nuclear-encoded, plastid-targeted proteome, which is transported across membranes by transit peptides and their equivalents.

Representative examples include the apicoplast in apicomplexan parasites such as Plasmodium, a non-photosynthetic relic essential for parasite survival and hosting pathways for fatty acid, isoprenoid, and heme biosynthesis. Other plastidlike systems arise from secondary or tertiary endosymbiosis, such as the chloroplast-derived plastids in chlorarachniophytes and cryptophytes, which can retain nucleomorphs—miniature nuclei from the algal endosymbiont—while performing limited biosynthetic functions. In some dinoflagellates and other protists, non-photosynthetic plastidlike compartments persist with plastid-targeting signals directing host-encoded proteins into them.

Evolutionarily, plastidlike organelles illustrate diverse endosymbiotic events, gene transfer to the host nucleus, and organelle genome reduction. Their study informs understanding of organelle biogenesis, metabolic integration, and potential targets for disease control when the lineage includes pathogens. Detection relies on ultrastructural features, plastid-type ribosomes, remnants of plastid genomes, and molecular signs of plastid-targeted protein import.

Overall, plastidlike denotes a broad class of evolutive remnants that resemble plastids by structure or metabolism, regardless of photosynthetic capacity, highlighting the plasticity of eukaryotic cell organization.