CC BY
31
44 • "PROTIST—2016
1 - Department of Environmental Life Sciences, Tohoku University, Japan
2 - Division of Environmental Photobiology, National Institute for Basic Biology, Japan
3 - Division of Morphogenesis, National Institute for Basic Biology, Japan
4 - Functional Genomics Facility, National Institute for Basic Biology, Japan [email protected]
Stable endosymbiotic relationship between cnida-rian animal and dinoflagellate Symbiodinium spp. is a prerequisite for sustaining coral reef ecosystem. Recent studies have shown that elevated seawater temperature can cause collapse of endosymbiosis by expulsion of the symbiotic algae from cnidarians, which is known as 'bleaching', and subsequent mass mortality. However, the technical difficulty in maintaining and using corals as material in laboratory has hampered further understanding of the molecular biology of the cnidarian-dinofla-gellate endosymbiosis. Here we show transcriptomic analyses using the symbiotic sea anemone Exaiptasia pallida (formerly Aiptasiaspp.), an emerging model cnidarian, in multiple culture conditions. The genome-wide gene expression profiles were analyzed by mapping the RNAseq reads from symbiotic and experimental apo-symbiotic anemones onto the host and endosymbiont genome sequences. A large portion of the genes differentially expressed in response to light and elevated temperature in the symbiotic and apo-symbiotic anemones was not overlapped and, in a number of cases, different members in a single gene family were activated between the symbiotic and apo-symbiotic anemones. These suggest that the anemones use distinct gene sets to respond to environmental changes depending on the symbiosis states with Symbiodinium. From the endosymbiont side, several photosynthesis-related genes associated with the photosystem II core assembly were detected to be down-regulated under the heat condition in hospite, which potentially affect the photodamage-induced stress responses. Overall, our data suggest that the endosymbiosis with Symbiodinium substantially affect the host's transcriptional profiles, potentially leading to the altered ecological contribution to the environment.
CHLOROPLAST DIVISION OF TETRASEL-MIS SP. IN THE FOOD VACUOLE OF MIXO-TROPHIC ALGAE RAPAZA VIRIDIS Maruyama M.1, Miyagishima S.2, Suzaki T.3, Kashiyama Y.14
1 - Fukui University of Technology
2 - National Institute of Genetics
3 - Kobe University
4 - Ritsumeikan University [email protected]
Rapaza viridis is a euglenoid that always possesses chloroplasts in cells without exception. R. viridis requires not only light but also a specific strain of green algae (Tetraselmis sp.) as its prey for their survival/growth, hence apparently being of obligate mixotrophy. Nonetheless, the degradative process of chloroplasts of the prey was barely observed. Furthermore, only trace amount of 132,173-cyclopheophorbide enols (CPEs), the non-phototoxic catabolites of chlorophylls, was produced along with the predation, indicating that only a small proportion of chlorophylls was actually discarded from the ingested chloroplasts. We thus investigated cell dynamics regarding ingested chloroplasts in R. viridis to understand the fate of the chloroplasts and chlorophylls contained therein. Unlike other phycophagic euglenoids, decrement of chlorophyll fluorescence from the ingested chloroplasts was rarely observed, and any evidence for digestive degradation of the chloroplasts was not recognized. Furthermore, the chloro-plastic eye-spots of Tetraselmis sp. became dispersed several hours after the ingestion and eventually disappeared. In the next hours, interestingly, the ingested chloroplasts became subdivided into more than several pieces with various sizes. Within a day, the unique, rough appearance of chloroplasts of Tetraselmis sp. in the DIC image became insignificant and changed into a rather smooth appearance that is no more distinguishable from those originally possessed by R. viridis. Afterward, the number of "chloroplasts" per cell began to decrease, suggesting progress of R. viridis cell divisions at this stage. We discuss the mechanism for the observed chloroplast division and the origin of "chloroplasts" of R. viridis.
HETEROGENEITY IN NUTRIENT UPTAKE BY INDIVIDUAL DINOFLAGELLATE CELLS REVEALED USING NanoSIMS Matantseva O.1, Vogts A.2, Voss M.2, Skarlato S.1
1 - Institute ofCytology RAS, St. Petersburg, Russia
2 - Institute for Baltic Sea Research Warnemuende, Germany
Dinoflagellates are one of the most successful groups of marine protists. Many photosynthetic dinoflagellates can utilize not only inorganic, but also organic compounds as nutrients, which is advantageous in eutrophied coastal zones. Therefore, nutritional physiology of these organisms receives much scientific attention. Usually it is studied by bulk approaches; however, the use of
