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Mitochondria and Plastids Evolved in Miniscule Plankton to Form Eye-like Structure

An eye-like structure called the ocelloid, found in warnowiid dinoflagellates, has long puzzled biologists. This structure resembles the eye of higher organisms to such a degree, that is was first assumed to be part of an animal the warnowiid had eaten. Now this small eukaryotic plankton has surprised scientists again – the warnowiid eye’s building blocks are mitochondria and plastids.

Scientists at the University of British Columbia used a combination of electron microscopy, tomography, isolated-organelle genomics, and single-cell genomics to show that the warnowiid eye is constructed from repurposed organelles. Interconnected mitochondria form the ocelloid cornea and interconnected plastids, photosynthetic organelles that originate from an endosymbiotic relationship between the warnowiid and red algae, form the retinal body. Gregory et al hypothesize that the plastid machinery that was once used to convert light into energy has been repurposed to detect light.

These findings demonstrate that organelles of different endosymbiotic origin can be assembled into complex structures to carry out a novel function. How warnowiids use ocelloids remains elusive as this plankton cannot be cultured in the laboratory. Gregory et al hope to learn more about this fascinating organelle to further our understanding of convergent evolution – the phenomenon that similar traits can evolve separately in several lineages.

Source: University of British Columbia

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