Understanding kleptoplasty in Sacoglossa (Heterobranchia, Gastropoda) - a cellular histochemical and genomic approach

囊舌藻是一个神秘的异枝藻类群，以其某些成员能够从藻类食物中吸收叶绿体（cps）而闻名，并且在没有额外进食的情况下存活数周和数月。最近的转录组分析拒绝了旧的假设，这表明藻类核基因组和蛞蝓核基因组之间的水平基因转移作为这种相互作用的基础。因此，cps的保留不能通过基因转移的遗传支持来解释。因此，新的假设必须转向cps和slug的相互作用和特定特性。在过去的几年里，我们对Sacoglossa的了解大大增加，包括系统发育关系，食物特异性，蛞蝓行为和光合能力的信息。这些信息解释了几个因素，提高cps的维持和蛞蝓的生存，但只有少数研究涉及细胞水平上的属性。以前的结果（包括我们自己的）表明，只有少数叶绿体类型的特定生存，特定时间的生存依赖于饥饿和食物供应，以及蛞蝓个体发育阶段的cps。本项目旨在阐明细胞水平上的cp掺入过程，并探索cp在蛞蝓消化腺细胞中的作用，特别是关于其作为长期能量储存装置的贡献，并具有在一定时间内增加营养价值的能力。这项研究将利用超微结构，免疫组织化学和共聚焦激光显微镜方法，以确定路径，每个纳入cp一旦摄入。定量方法（形态测量、定量真实的时间PCR（qPCR）和生化分析）将有助于阐明cps作为营养库的贡献。对基因表达的研究将有助于了解蛞蝓在不同饥饿阶段的生理和遗传特性。重点研究了姐妹类群Elysia timida和E.它们都以伞藻为食。E. timida可使cps功能性保留数月，而E. cornigera只能保留cps几个星期

Sacoglossa is an enigmatic heterobranch group, well known for some members ability to incorporate chloroplasts (cps) from their algal food and to survive weeks and months without additionally feeding. Recent transcriptome analyses reject old hypotheses, which suggested a horizontal gene transfer between the algal nuclear genome and the slugs nuclear genome as the basis for this interaction. Thus, the retention of cps cannot be explained by genetic support via gene transfer. New hypotheses must therefore shift to interactions and specific properties of cps and slugs. Our knowledge on Sacoglossa has increased considerably in the last years, including information on phylogenetic relationships, on food specificity, slug behaviour and photosynthetic capability. This information explains several factors that enhance cps maintenance and slugs survival, however only few studies have dealt with the properties on cellular level. Former results (including our own) indicate a specific survival of only few chloroplast types, a time specific survival of cps dependant on starvation and food availability, as well as slugs ontogenetic phase. This project aims to clarify the cp incorporation processon cellular level and explore the role of the cps in the slugs digestive gland cells, especially concerning their contribution as a long-term energetic storage device with the ability to increase nutritional value over a certain period of time. This investigation will utilize ultrastructural, immunohistochemical and confocal laser microscopical methods to determine the path each incorporated cp takes once ingested. Quantitative methods (morphometry, quantitative real time PCR (qPCR) and biochemical analyses) will help to elucidate the contribution of the cps as nutrional depots. Study of gene expression will help to understand physiological and genetic properties of the slugs during various starvation phases. We focus on sister-taxa, Elysia timida and E. cornigera, both of which feed on Acetabularia. E. timida can retain functional cps for months whereas E. cornigera can only retain cps for a few weeks