Differential Gene Expression Supports a Resource‐Intensive, Defensive Role for Colony Production in the Bloom‐Forming Haptophyte, Phaeocystis globosa

Abstract

Phaeocystis globosa forms dense, monospecific blooms in temperate, northern waters. Blooms are usually dominated by the colonial morphotype—nonflagellated cells embedded in a secreted mucilaginous mass. Colonial Phaeocystis blooms significantly affect food‐web structure and function and negatively impact fisheries and aquaculture, but factors regulating colony formation remain enigmatic. Destructive P. globosa blooms have been reported in tropical and subtropical regions more recently and warm‐water blooms could become more common with continued climate change and coastal eutrophication. We therefore assessed genetic pathways associated with colony formation by investigating differential gene expression between colonial and solitary cells of a warm‐water P. globosa strain. Our results illustrate a transcriptional shift in colonial cells with most of the differentially expressed genes downregulated, supporting a reallocation of resources associated with forming and maintaining colonies. Dimethylsulfide and acrylate production and pathogen interaction pathways were upregulated in colonial cells, suggesting a defensive role for producing colonies. We identify several protein kinase signaling pathways that may influence the transition between morphotypes, providing targets for future research into factors affecting colony formation. This study provides novel insights into genetic mechanisms involved in Phaeocystis colony formation and provides new evidence supporting a defensive role for Phaeocystis colonies.

Bacterial Composition Associated With Giant Colonies of the Harmful Algal Species Phaeocystis globosa

“…However, the role of the marine heterotrophic bacteria Labrenzia in DMSP producing and consuming has been demonstrated recently (Curson et al, 2017). In addition to serving as an osmolyte in many marine algae, including prymnesiophytes and dinoflagellates, DMSP and DMS also function as antioxidants under stressful conditions (e.g., high solar photon fluxes and nutrient limitation), which result in substantial increases in cellular DMSP and DMS concentrations (Sunda et al, 2002;Brisbin and Mitarai, 2019). Marine phytoplankton will encounter challenges caused by global change in the future, and as a result, cellular DMSP and DMS production may increase due to this stress.…”

Cytoklepty in the plankton: A host strategy to optimize the bioenergetic machinery of endosymbiotic algae

“…The uncoupling between cell-cycle progression and plastid division in symbiotic Phaeocystis suggests that the plastid-to-nucleus signal required to continue cell division is inhibited and deciphering the mechanism involved warrants further attention. Canonical cellsignaling pathways are a promising target for future work, as they have been implicated in mediating other endosymbioses as well as the morphological transformation between flagellate and colonial Phaeocystis cells (63,64). As this cytoklepty shares important similarities with kleptoplastidy and may represent an early intermediary step between photosymbiosis and more permanent incorporation of the photosynthetic machinery, further elucidation of the mechanisms involved should pave the way to a more complete understanding of how eukaryotes acquire new organelles.…”

Effects of Modified Clay on Phaeocystis globosa Growth and Colony Formation

“…The formation of colonies is of great biological and ecological importance for the lifecycle of P. globosa. The thin and tough matrix of these colonies provides a defence mechanism against predators, viruses and other unfavorable environmental factors [10][11][12][13][14]. Additionally, the colony can serve as a "granary" for the storage of large amounts of organic matter and nutrients, which can provide energy for colonial cells in nutrientlimited environments [15,16].…”