Taxonomic distribution and origins of the extended LHC (light-harvesting complex) antenna protein superfamily

<p>Abstract</p> <p>Background</p> <p>The extended light-harvesting complex (LHC) protein superfamily is a centerpiece of eukaryotic photosynthesis, comprising the LHC family and several families involved in photoprotection, like the LHC-like and the photosystem II subunit S (PSBS). The evolution of this complex superfamily has long remained elusive, partially due to previously missing families.</p> <p>Results</p> <p>In this study we present a meticulous search for LHC-like sequences in public genome and expressed sequence tag databases covering twelve representative photosynthetic eukaryotes from the three primary lineages of plants (Plantae): glaucophytes, red algae and green plants (Viridiplantae). By introducing a coherent classification of the different protein families based on both, hidden Markov model analyses and structural predictions, numerous new LHC-like sequences were identified and several new families were described, including the red lineage chlorophyll <it>a/b</it>-binding-like protein (RedCAP) family from red algae and diatoms. The test of alternative topologies of sequences of the highly conserved chlorophyll-binding core structure of LHC and PSBS proteins significantly supports the independent origins of LHC and PSBS families via two unrelated internal gene duplication events. This result was confirmed by the application of cluster likelihood mapping.</p> <p>Conclusions</p> <p>The independent evolution of LHC and PSBS families is supported by strong phylogenetic evidence. In addition, a possible origin of LHC and PSBS families from different homologous members of the stress-enhanced protein subfamily, a diverse and anciently paralogous group of two-helix proteins, seems likely. The new hypothesis for the evolution of the extended LHC protein superfamily proposed here is in agreement with the character evolution analysis that incorporates the distribution of families and subfamilies across taxonomic lineages. Intriguingly, stress-enhanced proteins, which are universally found in the genomes of green plants, red algae, glaucophytes and in diatoms with complex plastids, could represent an important and previously missing link in the evolution of the extended LHC protein superfamily.</p

High light acclimation in green microalgae in Non-Photochemical Quenching and Thermal Energy Dissipation In Plants, Algae and Cyanobacteria

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Photoprotective Mechanisms: Carotenoids

Environmental light can frequently be detrimental to the photosynthetic machinery of plants. This chapter provides an up-to-date overview of the targets of the photo-oxidative damage caused by light and the multiple functions of photosynthetic carotenoids that minimize it. Recently acquired knowledge on the localisation and distribution of carotenoids in the photosynthetic apparatus of plants is presented. Mechanisms that control the light harvesting process in the photosynthetic antenna of higher plants, via protective energy dissipation, are compared and discussed. The role of functional genomics approaches to the study of the multiple functions of carotenoids are highlighted. The significance of carotenoid structure and the physico-chemical properties that enable fine control over the photosynthetic light harvesting processes are analysed and discussed in order to explain the variety of their types