Name: Jennifer Dingman

Email: jennifer.dingman@unb.ca

Author: Jennifer E. Dingman*1 and Janice E. Lawrence1

Author affiliation: 1Department of Biology, University of New Brunswick, Fredericton, NB, Canada *Presenting Author

Abstract title: Programmed Cell Death Activated in Heterosigma akashiwo During Lytic Viral Infection

Absstract:

Despite their enormous production and turnover rates, the life and death strategies of phytoplankton are poorly understood. It was previously thought that, because of on-going cell division, single-celled phytoplankton do not die unless effected by external factors such as predator grazing or sedimentation. However, researchers have observed cell lysis, viral infection, autocatalytic cell death and caspase activation in phytoplankton, which suggests necrotic and programmed cell death (PCD) pathways may exist. This also suggests there may be additional factors controlling primary productivity, although very little is known about these other processes. In this study, the lytic infection cycle of HaNIV was examined in the bloom-forming raphidophyte Heterosigma akashiwo. The following PCD hallmarks were monitored during the 8-day infection: caspase activation, externalization of phosphatidylserine residues (PSR) and cell death. The presence of active caspase-8 and the proportion of cells with externalized PSR significantly increased at 72hr post inoculation (p=0.0037 and 0.0179, respectively) while cell number and relative fluorescence significantly decreased at 96hr post inoculation (p<0.0001). Caspase-8 activity and proportion of cells with externalized PSR peaked at 168Hr post inoculation after which the cultures completely lysed. The presence of active caspase-8 and externalization of PSR prior to culture decline in combination with previously reported nuclear ultrastructural changes is indicative that the PCD pathway is present in H. akashiwo.