Abstract
BackgroundLight harvesting complex (LHC) proteins function in photosynthesis by binding chlorophyll (Chl) and carotenoid molecules that absorb light and transfer the energy to the reaction center Chl of the photosystem. Most research has focused on LHCs of plants and chlorophytes that bind Chl a and b and extensive work on these proteins has uncovered a diversity of biochemical functions, expression patterns and amino acid sequences. We focus here on a less-studied family of LHCs that typically bind Chl a and c, and that are widely distributed in Chl c-containing and other algae. Previous phylogenetic analyses of these proteins suggested that individual algal lineages possess proteins from one or two subfamilies, and that most subfamilies are characteristic of a particular algal lineage, but genome-scale datasets had revealed that some species have multiple different forms of the gene. Such observations also suggested that there might have been an important influence of endosymbiosis in the evolution of LHCs.ResultsWe reconstruct a phylogeny of LHCs from Chl c-containing algae and related lineages using data from recent sequencing projects to give ~10-fold larger taxon sampling than previous studies. The phylogeny indicates that individual taxa possess proteins from multiple LHC subfamilies and that several LHC subfamilies are found in distantly related algal lineages. This phylogenetic pattern implies functional differentiation of the gene families, a hypothesis that is consistent with data on gene expression, carotenoid binding and physical associations with other LHCs. In all probability LHCs have undergone a complex history of evolution of function, gene transfer, and lineage-specific diversification.ConclusionThe analysis provides a strikingly different picture of LHC diversity than previous analyses of LHC evolution. Individual algal lineages possess proteins from multiple LHC subfamilies. Evolutionary relationships showed support for the hypothesized origin of Chl c plastids. This work also allows recent experimental findings about molecular function to be understood in a broader phylogenetic context.
Highlights
Light harvesting complex (LHC) proteins function in photosynthesis by binding chlorophyll (Chl) and carotenoid molecules that absorb light and transfer the energy to the reaction center Chl of the photosystem
Light harvesting complex (LHC) proteins are fundamental to oxygenic photosynthesis, and members of the LHC family are present in most photosynthetic eukaryotes, variation in nomenclature sometimes obscures their widespread occurrence (Table 1)
Overview of the Phylogeny To help ensure that the gene phylogeny was comprehensive, but bounded by objective criteria, sequences were selected by BLAST analysis with a relatively low threshold, and screened for the feasibility of endto-end alignment
Summary
Light harvesting complex (LHC) proteins function in photosynthesis by binding chlorophyll (Chl) and carotenoid molecules that absorb light and transfer the energy to the reaction center Chl of the photosystem. Previous phylogenetic analyses of these proteins suggested that individual algal lineages possess proteins from one or two subfamilies, and that most subfamilies are characteristic of a particular algal lineage, but genome-scale datasets had revealed that some species have multiple different forms of the gene Such observations suggested that there might have been an important influence of endosymbiosis in the evolution of LHCs. Light harvesting complex (LHC) proteins are fundamental to oxygenic photosynthesis, and members of the LHC family are present in most photosynthetic eukaryotes, variation in nomenclature sometimes obscures their widespread occurrence (Table 1). Light harvesting complex (LHC) proteins are fundamental to oxygenic photosynthesis, and members of the LHC family are present in most photosynthetic eukaryotes, variation in nomenclature sometimes obscures their widespread occurrence (Table 1) These transmembrane proteins bind chlorophyll (Chl) and carotenoid pigments which function to absorb light and transfer energy to the reaction center Chl of photosystems (PS) in the thylakoid membrane [1]. The biochemistry, physical interactions and molecular phylogeny of Systematic name
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