Light Stress Proteins in Viruses, Cyanobacteria and Photosynthetic Eukaryota

Plants in Nature frequently perceive environmental extremes such as light stress. To maintain their physiological functions under light stress conditions plants have developed different protection strategies that operate at morphological, anatomical and subcellular levels. The accumulation of light stress proteins from the ELIP (early light-induced protein) family can be considered to be a part of such photoprotective responses. ELIPs are distant relatives of the chlorophyll a/b-binding proteins of photosystem I and II that accumulate only transiently in thylakoid membranes under certain physiological stress conditions. Based on predicted secondary structure ELIP family members are divided into three-helix ELIPs, two-helix SEPs (stress-enhanced proteins) and one-helix OHPs (one-helix proteins), called also HLIPs (high light-induced proteins) or SCPs (small chlorophyll-binding-like proteins) in cyanobacteria and viruses. It is believed that these proteins play a protective role within the chloroplast under light stress conditions either by transient binding of free chlorophylls and preventing the formation of free radicals and/or by acting as sinks for excitation energy. Expanding functional genomics provided new tools for the identification of genes and proteins structurally and/or functionally related to ELIP family members that escaped previous detection by classical molecular biology or biochemical methods. This chapter provides an overview of “classical” ELIP family members, discusses their evolution and photoprotective functions and introduces novel types of ELIP-like proteins in algae and land plants.