Central Project

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Light has major impacts on algae (i) serving as energy source for photosynthesis, (ii) triggering behavioral responses mediated by light perception via photoreceptors and (iii) entraining their circadian clocks by light-dark cycles. The recent sequencing of the genomes of the green alga Chlamydomonas reinhardtii and of the diatom Phaeodactylum tricornutum by the Joint Genome Institute (JGIDepartment of Energy, USA) and the international annotation effort allowed to perform comparative genome approaches as well as proteomic analysis, e.g. of the eyespot apparatus of Chlamydomonas, a primordial visual system. Along with the genome and proteome approaches, several molecular genetic tools have been developed on an international basis in the past years for these two algae. Altogether, these efforts provide novel information and represent an efficient platform to perform an in-depth characterization of relevant proteins involved in lightdriven pathways. Such an effort requires the collaboration of scientists who are experienced in physiology, molecular biology and/or biophysics. Within the Frame of this research group, we have assembled such an interdisciplinary team and want to focus on novel aspects of light-driven reactions from light absorption to physiological responses that are typical for either of the two species and where profound information about the processes is still lacking or is very limited. One focus will be on the functional and biophysical characterization of photoreceptors in C. reinhardtii that are involved in light- and circadian signaling. Blue light has been shown by physiological studies to be relevant for entraining the clock of Chlamydomonas. Potential candidates are plant- and animal-like cryptochromes, channelrhodopsin 2 and phototropin. Another focus will be on the light-signalingcascade in C. reinhardtii involving channelrhodopsins and Ca2+-binding Proteins located in the eyespot apparatus that can mediate absorbed light information. Thereby, a SOUL heme-binding protein (SOUL3) that was also found in the eyespot proteome will be of further interest. SOUL was first described in vertebrates where its mRNA is specifically expressed in the retina and pineal gland (Zylka and Reppert, 1999). Moreover, enzyme-like rhodopsins containing His-kinase and response regulator domains, whose function is completely unknown so far, will be under investigation. In the diatom P. tricornutum, we will analyze for the first time the function of the cryptochromes as well as of the diatom aureochromes. Our studies will also include an understanding of the mechanism of the light Regulation of diatom photosynthesis on different levels, i.e. the light-dependent synthesis of relevant proteins, as well as redox mediated regulation processes. Albeit diatoms contribute up to 20% to the primary production on Earth, little is known about their photosynthesis in comparison to the green lineage. This combined interdisciplinary approach will give a detailed view about specific light-driven reactions from the absorption of light to the function of the involved signaling cascade members and their relevance in different biological processes in the two chosen model algae.