Comparative genomic analysis illustrates evolutionary dynamics of multisubunit tethering complexes across green algal diversity

The chlorophyte algae are a dominant group of photosynthetic eukaryotes. Although many are photoautotrophs, there are also mixotrophs, heterotrophs, and even parasites. The physical characteristics of green algae are also highly diverse, varying greatly in size, shape, and habitat. Given this morphological and trophic diversity, we postulated that diversity may also exist in the protein components controlling intracellular movement of material by vesicular transport. One such set is the multisubunit tethering complexes (MTCs)—components regulating cargo delivery. As they span endomembrane organelles and are well-conserved across eukaryotes, MTCs should be a good proxy for assessing the evolutionary dynamics across the diversity of Chlorophyta. Our results reveal that while green algae carry a generally conserved and unduplicated complement of MTCs, some intriguing variation exists. Notably, we identified incomplete sets of TRAPPII, exocyst, and HOPS/CORVET components in all Mamiellophyceae, and what is more, not a single subunit of Dsl1 was found in Cymbomonas tetramitiformis. As the absence of Dsl1 has been correlated with having unusual peroxisomes, we searched for peroxisome biogenesis machinery, finding very few components in Cymbomonas, suggestive of peroxisome degeneration. Overall, we demonstrate conservation of MTCs across green algae, but with notable taxon-specific losses suggestive of unusual endomembrane systems.