Stress responses of the oil-producing green microalgaBotryococcus brauniiRace B

Abstract

Plants react to biotic and abiotic stresses with a variety of responses including the production of reactive oxygen species (ROS), which may result in programmed cell death (PCD). The mechanisms underlying ROS production and PCD have not been well studied in microalgae. Here, we analyzed ROS accumulation, biomass accumulation, and hydrocarbon production in the colony-forming green microalgaBotryococcus brauniiin response to several stress inducers such as NaCl, NaHCO3, salicylic acid (SA), methyl jasmonate, and acetic acid. We also identified and cloned a single cDNA for theB. brauniiortholog of theArabidopsisgenedefender against cell death 1(DAD1),a gene that is directly involved in PCD regulation. The function ofB. braunii DAD1was assessed by a complementation assay of the yeast knockout line of theDAD1ortholog, oligosaccharyl transferase 2. Additionally, we found thatDAD1transcription was induced in response to SA at short times. These results suggest thatB. brauniiresponds to stresses by mechanisms similar to those in land plants and other  organisms.