Abstract
BackgroundThe Synurophyceae is one of most important photosynthetic stramenopile algal lineages in freshwater ecosystems. They are characterized by siliceous scales covering the cell or colony surface and possess plastids of red-algal secondary or tertiary endosymbiotic origin. Despite their ecological and evolutionary significance, the relationships amongst extant Synurophyceae are unclear, as is their relationship to most other stramenopiles.ResultsHere we report a comparative analysis of plastid genomes sequenced from five representative synurophycean algae. Most of these plastid genomes are highly conserved with respect to genome structure and coding capacity, with the exception of gene re-arrangements and partial duplications at the boundary of the inverted repeat and single-copy regions. Several lineage-specific gene loss/gain events and intron insertions were detected (e.g., cemA, dnaB, syfB, and trnL).ConclusionsUnexpectedly, the cemA gene of Synurophyceae shows a strong relationship with sequences from members of the green-algal lineage, suggesting the occurrence of a lateral gene transfer event. Using a molecular clock approach based on silica fossil record data, we infer the timing of genome re-arrangement and gene gain/loss events in the plastid genomes of Synurophyceae.
Highlights
The Synurophyceae, a class of photosynthetic stramenopile algae, is a morphologically diverse lineage with plastids derived from red algae via secondary or tertiary endosymbiosis
Our results provides important insights into the evolutionary history of organelle genomes via lateral gene transfer (LGT) from green-algal lineages into the Synurophyceae, as well as divergence time estimates using molecular clock approaches based on silica fossil records
The trnRUCU in S. petersenii, S. uvella, and M. splendens and trnEUUC in N. volvocina is present as a pseudogene; it has a low hidden Markov model score (HMM score = 0) and a secondary structure-only score (2Str Score < 40) predicted by tRNAscan-SE
Summary
The Synurophyceae, a class of photosynthetic stramenopile (or heterokont) algae, is a morphologically diverse lineage with plastids derived from red algae via secondary or tertiary endosymbiosis. They are motile organisms with two parallel emergent flagella, one or two plastids, a cell coat in which the siliceous scales cover the entire cell, and lack of an eyespot [1, 2]. The Synurophyceae is one of most important photosynthetic stramenopile algal lineages in freshwater ecosystems They are characterized by siliceous scales covering the cell or colony surface and possess plastids of redalgal secondary or tertiary endosymbiotic origin. Despite their ecological and evolutionary significance, the relationships amongst extant Synurophyceae are unclear, as is their relationship to most other stramenopiles
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