Transcriptome sequencing of Heterosigma akashiwo on a parabolic flight

Many species of phytoplankton are motile and migrate in response to gravity. Despite the minute size of the individual organisms, their large numbers and fundamental role as the base of nearly every aquatic food web makes these some of the most important migrations on Earth. Recently, we have discovered that periodic changes in the orientation of the organisms relative to gravity can have a major impact on phytoplankton migration, by inducing an upward-migrating population to split (50:50) in two subpopulations: one that continues to swim upwards and one that instead swims downwards (Sengupta et al, 2017). This behavior was interpreted as a response to perceived changes of gravity through small scale turbulence flipping the cells around every few tens of seconds. We have brought our model species, Heterosigma akashiwo, on board the 2nd Swiss Parabolic Flight to test the hypothesis that the trigger for this response are changes in the gravity vector. Apart from direct visualization on board, we have taken samples for transcriptomic analysis at an early (15 min of gravity perturbations) and a late timepoint (50 min of gravity perturbations) during the flight with the aim to investigate transcriptomic reactions of H. akashiwo to the gravity stress. An parallel ground experiment mimicking times, sample handling, and temperatures on the flight served as control.