Understanding the cellular role of aureochromes, a new type of blue light photoreceptors, in diatoms

硅藻是单细胞光自养藻类，在浮游和底栖水生群落中非常成功。此外，它们代表着特殊的进化嵌合细胞，因为它们是通过将一种真核藻吸收到另一种真核细胞中而进化出来的。因此，硅藻的遗传背景与绿藻和植物不同。硅藻和相关藻类中的硅藻具有蓝光感受器，称为金色，这种感光器只在这一组中发现。与其他已知的光感受器不同，金色蛋白是光激活的转录因子，具有LOV结构域和DNA结合的bZIP结构域。我们最近对硅藻三角褐指藻的研究表明：(I)这种藻类具有四种不同的金色蛋白，(Ii)金色蛋白对于光适应是重要的，以及(Iii)敲除单个金色蛋白基因(Ptaureo1a)会导致细胞从红光转移到蓝光时转录调控显著和大量减少。因此，我们推测PtAUREO1a可能是蓝光反应的一个“主开关”。因此，在这个项目中，我们希望通过PtAureo基因敲除突变体来阐明金色蛋白在硅藻中的细胞功能作用。第一个子项目将研究PtAUREO1c和2个KO突变体在红/蓝光转换后的转录反应。在广泛的方法中，我们将研究可用的PtAureo基因敲除系的生理学，以了解缺乏各自的光感受器的具体影响。然后，我们将研究不同光照条件的作用，以及限制因素如氮剥夺对WT和突变株系竞争力的作用。最后，在代谢组学的方法中，我们想要调查在基因敲除的突变体中，它们的竞争能力是否受到损害。在第二个子项目中，我们将试图通过鉴定金色结合位点、通过酵母1-杂交方法研究PtAureo/启动子结合、金色二聚体的形成以及共结合因子的鉴定来揭示PTAUREO1a的功能。这个项目将基于两个独立研究小组的密切合作，这两个小组开创了硅藻分子和生理特征领域的先河，它努力更好地理解硅藻如何感知光，以及这种信息如何转化为细胞反应。

Diatoms are unicellular photoautotrophic algae and extremely successful in planktonic and benthic aquatic communities. In addition, they represent peculiar evolutionary chimeric cells, as they evolved by the uptake of a eukaryotic alga into another eukaryotic cell. Accordingly, diatoms have a different genetic background than green algae and plants. Diatoms and related algae within the group of Stramenopiles possess blue light photoreceptors named aureochromes that are found only within this group. In contrast to other know photoreceptors, aureochromes are light-activated transcription factors possessing a LOV domain as well as a DNA-binding bZIP domain. Our recent work on the diatom Phaeodactylum tricornutum demonstrates (i) that this alga possesses four different aureochromes, (ii) that aureochromes are important for photoacclimation, and (iii) that knocking out a single aureochrome gene (PtAureo1a) results in a dramatic and massive reduction of transcriptomic regulation when the cells are transferred from red light to blue light. Therefore, we postulate that PtAUREO1a may be one “master switch” for blue light responses. Accordingly, in this project, we want to elucidate the functional cellular role of Aureochromes in diatoms using PtAureo knockout mutants. The first subproject will study the transcriptomic response of PtAUREO1c and 2 KO mutants after a red/blue light shift. In a broad approach, we will study the physiology of the available PtAureo knockout lines to understand the specific impact of the lack of the respective photoreceptors. Then we will investigate the role of different light conditions, and the role of limiting factors like N deprivation for competitiveness of WT and mutant lines. Finally, in a metabolomics approach, we want to investigate whether in the knockout mutants are impaired in their competitive strength. In the second subproject, we will try to unravel the functionality of PTAUREO1a by identifying aureochrome binding sites, investigating PtAureo/promotor binding via yeast 1-hybrid approaches, aureochrome dimer formation, as well as identification of co-binding factors. This project will be based on a very tight collaboration of two independent research groups that have pioneered the field of molecular and physiological characterization of diatoms, and it strives for a better understanding how diatoms sense light and how this information is converted into a cellular response.