Journal Article

Phylogeny of Galactolipid Synthase Homologs Together with their Enzymatic Analyses Revealed a Possible Origin and Divergence Time for Photosynthetic Membrane Biogenesis

Yuichi Yuzawa, Hidenori Nishihara, Tsuyoshi Haraguchi, Shinji Masuda, Mie Shimojima, Atsushi Shimoyama, Hideya Yuasa, Norihiro Okada and Hiroyuki Ohta

in DNA Research

Published on behalf of Kazusa DNA Research Institute

Volume 19, issue 1, pages 91-102
Published in print February 2012 | ISSN: 1340-2838
Published online December 2011 | e-ISSN: 1756-1663 | DOI: http://dx.doi.org/10.1093/dnares/dsr044

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The photosynthetic membranes of cyanobacteria and chloroplasts of higher plants have remarkably similar lipid compositions. In particular, thylakoid membranes of both cyanobacteria and chloroplasts are composed of galactolipids, of which monogalactosyldiacylglycerol (MGDG) is the most abundant, although MGDG biosynthetic pathways are different in these organisms. Comprehensive phylogenetic analysis revealed that MGDG synthase (MGD) homologs of filamentous anoxygenic phototrophs Chloroflexi have a close relationship with MGDs of Viridiplantae (green algae and land plants). Furthermore, analyses for the sugar specificity and anomeric configuration of the sugar head groups revealed that one of the MGD homologs exhibited a true MGDG synthetic activity. We therefore presumed that higher plant MGDs are derived from this ancestral type of MGD genes, and genes involved in membrane biogenesis and photosystems have been already functionally associated at least at the time of Chloroflexi divergence. As MGD gene duplication is an important event during plastid evolution, we also estimated the divergence time of type A and B MGDs. Our analysis indicated that these genes diverged ∼323 million years ago, when Spermatophyta (seed plants) were appearing. Galactolipid synthesis is required to produce photosynthetic membranes; based on MGD gene sequences and activities, we have proposed a novel evolutionary model that has increased our understanding of photosynthesis evolution.

Keywords: monogalactosyldiacylglycerol; MGDG synthase; galactolipid; Roseiflexus castenholzii; plastid evolution

Journal Article.  6026 words.  Illustrated.

Subjects: Genetics and Genomics

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