The molecular basis of high light photoacclimation in diatoms

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The photosynthetic efficiency and productivity of diatoms may depend on the light environment which can be highly variable in aquatic ecosystems. To maintain optimal photosynthesis in a permanently changing environment, diatoms have evolved a number of regulatory mechanisms. The photoprotective NPQ (non-photochemical fluorescence quenching) process allows the plastid to safely dissipate the excess energy absorbed during a light stress. The extent of NPQ can be rather high in diatoms. Xanthophyll pigments and specific light-harvesting complex (LHC) polypeptides are necessary for the NPQ mechanism. We want to address the question how the organization and composition (polypeptide and pigment) of the LHC antenna enable the diatoms to cope with the stressful increase of light intensity. Especially, we want to gain knowledge on the LHC polypeptide(s) involved in the response of the cells to high light, and to identify the special LHC antenna polypeptide(s) possibly involved in the control of the NPQ process. In this context, we will focus on a particular group of these polypeptides: the High Light Induced Proteins (HLlPs). In diatoms, nothing is known concerning their location in the LHC antenna, their regulation as a function of light at the gene and protein levels, and their role in the physiological response of the diatoms to high light stress. We will study these aspects of the acclimation to high light in diatoms by coupling a proteomic approach on the LHC system, gene expression analysis versus light, in vivo genetic modulation of HLIPs and physiological characterization.