Interplay between carbon concentrating mechanism and osmoregulation / ion-regulation in Charophytes: chance or obstacle for adaptation to terrestrial conditions? (ICOR)

轮藻是属于链藻门的沉水植物，链藻门也包括所有的陆生植物。轮藻纲与双星藻纲和鞘毛藻纲一起组成ZCC分支，是陆地植物的共同祖先。轮藻是最复杂的链霉菌藻类，其表现出被认为是成功定殖陆生生境的强制性特征（例如功能性假根、配子囊包膜、皮层化）。因此，它们是一个重要的垫脚石，值得详细研究，以了解地球化的机制。无机碳（Ci）有效性的急剧下降可能是陆地化过程中最引人注目的挑战之一。被动扩散的CO2是无法满足复杂的水生真核光合自养生物在最近的低大气pCO2条件下的光合需求。因此，真核藻类通常采用复杂的碳浓缩机制（CCM）来富集Rubisco附近的CO2。然而，轮藻中CCM的存在和功能是不确定的。此外，pH值和离子驯化和Ci收购之间的强烈干扰是expected.In初步实验中，我们建立了轮藻在规定的条件下培养系统。选定的物种能够在pCO2、盐度和pH值的广泛范围内生长。对于该项目，我们将集中在轮藻braunii，因为其可用的良好注释的基因组序列提供了一个坚实的基础，计划的分子工作。在C. braunii基因组中检测到许多可能编码真核模式藻如莱茵衣藻CCM相关蛋白的基因。braunii执行CCM。为此，我们将比较完整的C。braunii及其羧化酶Rubisco。将在不同的CO2和pH水平下培养拟南芥，以研究它是否可以通过改变光合CO2亲和力来响应不同的Ci水平。将通过qPCR分析轮藻CCM中所涉及的所选基因的表达。最后，在C. braunii在不同盐度下培养。总的来说，我们的目标是找出轮藻是否进行CCM，哪些基因可能参与这一过程，以及在多大程度上它与周围沃茨中不同的离子关系相互作用。

Charophytes are submerged macrophytes belonging to the Streptophyta, a clade which also include all land plants. Together with the Zygnematophyceae and the Coleochaetophycae, Charophyceae form the ZCC clade, from which the common ancestor of land plants evolved. Charophytes are the most complex streptophyte algae, which exhibit features thought to be mandatory for successful colonization of the terrestrial habitat (e.g. functional rhizoids, gametangia envelopes, cortication). Hence, they represent an important stepping stone worth being investigated in detail in order to understand the mechanisms of terrestrialization. The drastic decline in availability of inorganic carbon (Ci) was probably one of the most striking challenge during terrestrialization. Passive diffusion of CO2 is unable to meet the photosynthetic demand of complex aquatic eukaryotic photoautotrophs at the recent low atmospheric pCO2 conditions. Therefore, eukaryotic algae usually employ sophisticated carbon-concentrating mechanisms (CCMs) to enrich CO2 in the vicinity of Rubisco. However, the existence and function of a CCM in Charophytes is uncertain. Moreover, s strong interference between pH and ion acclimation and Ci acquisition is anticipated.In preliminary experiments we established cultivation systems for Charophytes under defined conditions. Selected species are able to grow under a wide range of pCO2, salinity and pH levels. For the project we will concentrate on Chara braunii, because its available well-annotated genome sequence provides a solid base for the planned molecular work. Searches in the C. braunii genome resulted in the detection of many genes that potentially encode proteins involved in the CCM of eukaryotic model algae such as Chlamydomonas reinhardtii.The initial aim of this proposal is to unravel whether or not C. braunii performs a CCM. For this purpose, we will compare the CO2 affinities of intact C. braunii and its carboxylating enzyme Rubisco. The alga will be cultivated under different CO2 and pH levels to investigate if it can respond to different Ci levels by changing the photosynthetic CO2 affinity. The expression of selected genes putatively involved in Chara CCM will be analyzed by qPCR. Finally, the interaction of Ci and ion acclimation will be investigated in C. braunii after cultivation at different salinities. Collectively, we aim to find out if Charophytes perform a CCM, which genes may be involved in this process, and, how far it is interacting to different ionic relations in thesurrounding waters.