Gene Expression Changes of Phytoplankton Communities During a Dinoflagellate Bloom in East China Sea

Prorocentrum donghaiense is a typical dinoflagellate species which has caused massive red tides in East China Sea from April to May nearly annually. It is very challenging to identify the change of community composition and ecological function of phytoplankton community in situ. In this study, we used comparative metatranscriptomics on a time-serial samples in the course of P. donghaiense bloom development in East China Sea, and also conducted RNA-seq for spliced leader-based dinoflagellate-specific bloom samples, and laboratory-cultured P. donghaiense. Microscopic counting, 18S sequencing and transcripts data together revealed the major dominant group changed from diatoms to dinoflagellates both in abundance and transcriptional activity. The most active metabolic pathway of community was shifted from diatom carbohydrate metabolism, protein processing and other processes to dinoflagellate photosynthesis and ATP synthesis. Next, we focused on the remarkably up-regulated genes in P. donghaiense during the bloom, and found that they were mainly involved in energy metabolism, photosynthesis, nutrient acquisition, plant-microbe interaction and sexual reproduction. Among these, meiosis and proton pump rhodopsin genes were up-regulated by up to 100 and 6-97 folds, respectively during the bloom. All these results indicate the dynamic of both community structure and shift of major metabolic functional pathway due to ambient environmental changes, and reveal a comprehensive strategy in P. donghaiense to outcompete coexisting phytoplanktons in the environment, with rhodopsin-based energy acquisition and meiosis-based reproduction apparently as key drivers of rapid proliferation and bloom formation by this species.