The family of light-harvesting chlorophyll a/b-binding proteins in higher plants and green algae is composed of more than 20 different members associated with photosystem I and II. In addition, several distant relatives of this family with conserved chlorophyll-binding residues and a transient expression pattern related to various stress conditions have been reported. These distant relatives include: three-helix Elips ( early light-induced proteins) and related proteins, two-helix Seps (stress-enhanced proteins) and one-helix Ohps (one-helix proteins). While Elips are not detected under ambient light conditions, a significant amount of Seps and Ohps is present in the absence of light stress but their level increases drastically after exposure of leaves to high intensity light. In the past years our interest was focused on two such proteins, Sep2 and Ohp2. We would like to continue studies on location and function(s) of these proteins in Arabidopsis thaliana and broaden our analysis by including two additional members, Sep3 and Ohp1. We plan the overexpression and raising polyclonal antibodies for Sep3 and Ohp1 and reconstitution of overexpressed proteins with isolated pigments. Localization studies will be performed by subfractionation of thylakoid membranes and protein-protein interaction will be analyzed using crosslinking or a surface plasmon resonance technology (Biacore). Reverse genetics (analysis of "knock out", "knock down" mutants and transgenics) will be applied to unravel the function of these proteins in the chloroplast.