Molecular mechanisms during food acquisition and gliding locomotion in viridiraptorid amoeboflagellates - a transcriptomic study of Orciraptor agilis (Cercozoa, Rhizaria)

Viridiraptoridae是最近发现的一个吞噬性淡水鞭毛虫家族，其成员有能力穿透绿藻的细胞壁，以利用其细胞内容物作为食物。这些高度特化的“原生质体捕食者”的关键能力是纤维素细胞壁聚合物的局部降解，这种降解以一种明确的、特定物种的模式发生。随后的食物摄取，即藻类质体的提取或藻类细胞的入侵，涉及细胞骨架结构和功能的变化。在进食事件之间，移动的病毒状细胞表现出以鞭毛为基础的滑行运动，这是一个从不同系统发育关系的鞭毛中已知的运动过程，但研究很少。细胞壁穿孔，猎物细胞入侵和滑翔运动是三种迷人的，但尚未探索的现象在viridiraptorids。因此，我打算探索1)细胞壁降解酶，2)肌动蛋白结合蛋白，以及3)与微管相互作用的运动蛋白。这将通过比较转录组学方法和生化方法的选择来完成。我的目的是阐明上述过程的潜在分子机制，重点是涉及细胞壁裂解的碳水化合物活性酶。通过这一提议，我希望通过遗传和生化方法为单细胞“原生质体取食者”的酶细胞壁降解提供实验证据，表征候选酶，并探索与取食和运动有关的结构和产生力的细胞骨架蛋白。除了对viridiraptorids功能的具体见解外，这项工作还应该有助于提高对真核超群根瘤菌的基因组知识。

The Viridiraptoridae is a recently discovered family of phagotrophic freshwater flagellates, whose members have the ability to penetrate the cell walls of green algae in order to exploit their cell content as food. The key ability of these highly specialised 'protoplast feeders' is the local degradation of cellulosic cell wall polymers, which takes place in a well-defined and species-specific pattern. The subsequent food uptake, i.e. the extraction of the algal plastid or the invasion of the algal cell, involves changes in cytoskeletal architecture and function. Between feeding events, mobile viridiraptorid cells display flagella-based gliding motility, a still poorly studied locomotory process known from flagellates of diverse phylogenetic affiliation. Cell wall perforation, prey cell invasion and gliding motility are three fascinating, yet unexplored phenomena in viridiraptorids. Therefore, I intend to explore 1) cell wall degrading enzymes, 2) actin-binding proteins, and 3) motor proteins interacting with microtubules in the viridiraptorid Orciraptor agilis. This will be done with a comparative transcriptomic approach and a selection of biochemical methods. My aim is to shed light on the underlying molecular machinery of the above mentioned processes with a focus on carbohydrate-active enzymes involved in cell wall lysis. With this proposal I expect to provide experimental evidence for enzymatic cell wall degradation in unicellular 'protoplast feeders' with genetic and biochemical methods, to characterise candidate enzymes, and to explore the repertoire of structural and force-generating cytoskeletal proteins involved in feeding and locomotion. Besides specific insights into the functioning of viridiraptorids, this work should also contribute to enhance genomic knowledge about the yet understudied eukaryotic supergroup Rhizaria in general.