A light-triggered behavioural switch in cyanobacterial motility

蓝藻是执行类似植物的光合作用的光养原核生物。它们是所有植物和藻类叶绿体的祖先。除了将它们用作氧合光合作用的模式生物外，由于它们在生物技术应用方面的潜力，公众的兴趣也越来越大。像所有的光养生物一样，光感应对于蓝藻适应不同的环境条件至关重要。因此，它们必须选择最佳的光照条件来吸收光子进行光合作用能量供应，同时避免强光和紫外光胁迫。这就需要有效的适应策略，以便在不同的光照条件下生长。集胞藻的光感受器Cph2PCC 6803通过拥有两个不同的感光模块来感知四种不同的颜色。光信号被传递到酶活性效应器模块，该效应器模块合成或降解第二信使分子c-di-GMP。根据这种分子的浓度，蓝藻决定是向光源移动还是诱导生物膜形成。我们已经证明，多结构域传感器Cph2在蓝光下改变蓝藻细胞中c-di-GMP的水平，从而抑制对这些不利光条件的趋光性。虽然红/远红外吸收光敏色素组件的结构已经解决，但我们仍然不了解这一部分光开关的生物学功能。在项目提案中，我们想要阐明Cph2感应的不同光信号是如何整合并传递到控制蓝藻运动的c-di-GMP相关信号转导链的下游组件的。此外，我们还想鉴定未知的c-di-GMP效应蛋白，并分析它们在运动调节中的作用。我们将使用重组蛋白质的光谱分析、蛋白质相互作用研究、光遗传工具和光趋光性测试来揭示蓝藻模式菌株中基于Cph2的信号过程的潜在分子机制。

Cyanobacteria are phototrophic prokaryotes performing plant-like photosynthesis. They are the ancestors of all plant and algae chloroplasts. Besides using them as model organisms for oxygenic photosynthesis there is an increasing interest in the public because of their potential for biotechnological applications. Like for all phototrophs light sensing is of crucial importance for cyanobacteria to acclimate to different environmental conditions. Accordingly, they have to choose the optimal light conditions to absorb photons for photosynthetic energy supply and at the same time to avoid high- and UV-light stress. This requires efficient acclimation strategies for grow under different light conditions. The photoreceptor Cph2 from Synechocystis sp. PCC 6803 senses four different colours by harbouring two distinct photosensory modules. The light signals are transduced to the enzymatically active effector modules which synthesize or degrade the second messenger molecule c-di-GMP. Depending on the concentration of this molecule cyanobacteria decide whether to move towards a light source or to induce biofilm formation. We have demonstrated that the multi-domain sensor Cph2 alters the c-di-GMP level in cyanobacterial cells under blue light, thus inhibiting phototaxis towards these unfavourable light conditions. Though the structure of the red/far-red absorbing phytochrome module has been solved, we still do not understand the biological function of this part of the light switch. In the project proposal we want to elucidate how the different light signals sensed by Cph2 are integrated and transmitted to downstream components of a c-di-GMP related signal transduction chain that controls cyanobacterial motility. Further we want to identify the unknown c-di-GMP effector proteins and to analyze their roles in regulating motility. We will use spectroscopic analysis of recombinant proteins, protein interaction studies, optogenetic tools and phototaxis tests with various mutant strains of regulatory and structural elements to unravel the underlying molecular mechanism of Cph2 based signaling processes in the cyanobacterial model strain.