Transcriptomic and photophysiological responses to light stress in Bigelowiella natans

Abstract

Chlorarachniophytes, a group of marine unicellular amoeboflagellates, have acquired their plastid secondarily from a green alga transferring photosynthesis into the heterotrophic Rhizarian host. The evolutionary integration of organisms over time must coordinate gene expression to regulate stress responses. However, the light response mechanism has not been studied in chlorarachniophytes. I conducted an RNA-seq experiment to identify transcriptome changes under high (HL) or very-low (VL) light stress, in the model chlorarachniophyte, Bigelowiella natans. Under HL, genes involved in primary metabolism and detoxification increased, while VL reduced expression of genes in carbon metabolism and photosynthesis. The light-harvesting complex (LHC) genes with diverse origins from green and red algae were highly responsive to light stress. Two classes of LHCs were over-expressed only in HL, suggesting a role in photoprotective mechanisms like non-photochemical quenching. Together, B. natans displays distinct acclimation strategies that incorporated endosymbiont and host regulatory frameworks to cope with light stress.