Sterol Composition and Biosynthetic Genes of Vitrella brassicaformis, a Recently Discovered Chromerid: Comparison to Chromera velia and Phylogenetic Relationship with Apicomplexan Parasites

Abstract

Vitrella brassicaformis is the second discovered species in the Chromerida, and first in the family Vitrellaceae. Chromera velia, the first discovered species, forms an independent photosynthetic lineage with V. brassicaformis, and both are closely related to peridinin-containing dinoflagellates and nonphotosynthetic apicomplexans; both also show phylogenetic closeness with red algal plastids. We have utilized gas chromatography/mass spectrometry to identify two free sterols, 24-ethylcholest-5-en-3β-ol, and a minor unknown sterol which appeared to be a C(28:4) compound. We have also used RNA Seq analysis to identify seven genes found in the nonmevalonate/methylerythritol pathway (MEP) for sterol biosynthesis. Subsequent genome analysis of V. brassicaformis showed the presence of two mevalonate (MVA) pathway genes, though the genes were not observed in the transcriptome analysis. Transcripts from four genes (dxr, ispf, ispd, and idi) were selected and translated into proteins to study the phylogenetic relationship of sterol biosynthesis in V. brassicaformis and C. velia to other groups of algae and apicomplexans. On the basis of our genomic and transcriptomic analyses, we hypothesize that the MEP pathway was the primary pathway that apicomplexans used for sterol biosynthesis before they lost their sterol biosynthesis ability, although contribution of the MVA pathway cannot be discounted.

Sterols of morphologically distinct, okadaic acid‐producing Prorocentrum texanum var. texanum and var. cuspidatum isolated from the Gulf of Mexico

“…They also provide an interesting test case to compare another phenotypic trait beyond morphology [vs. the genetic identity as based on five genes by Henrichs et al, 2013]. To date, full pathway characterization of the genes for sterol biosynthesis (in a pathway that possesses approximately twenty genes) has only been achieved in model organisms such as the yeast Saccharomyces cerevisiae (Jordá & Puig, 2020) and the plant Arabidopsis thaliana (Du et al, 2022)—the comparable genes and enzymes (including the regulation of both) needed to synthesize the entire suite of sterols in any dinoflagellate are simply not known to completeness because at this point in time only a small number of the early pathway genes for sterol biosynthesis in dinoflagellates have been observed in a broad dinoflagellate character trait study (Janouškovec et al, 2014) and a study on the chromerid Vitrella brassicaformis (Khadka et al, 2015). Therefore, the sterols themselves produced by dinoflagellates, including those within the genus Prorocentrum , provide an array of quantifiable phenotypic end products with chemotaxonomic utility.…”