Effect of High Light Intensity on Polyketide Synthase Gene Expression in the Toxic Dinoflagellate, Karenia brevis

Abstract

Karenia brevis is the toxic dinoflagellate endemic to the Gulf of Mexico that causes detrimental human health, environmental, and economic impacts through the production of brevetoxins. Brevetoxins are polyketide compounds produced by polyketide synthase enzymes (PKS), but no gene or protein has been linked to their biosynthesis. Previous work on two PKS proteins, KB2006 and KB5299, suggests a link between chloroplast physiology and toxicity. To test the effect of high light (HL) intensity on PKS gene expression in NTB, 1‐liter cultures were exposed to HL treatment (~ 100 μmol photons m‐2s‐1 ) after reaching mid‐log phase in control light intensity (~ 60 μmol photons m‐2s‐1 ). Samples for cell counts and gene expression were taken at T0 (prior to HL treatment) and T6 (6 days post HL treatment) for control and HL cultures. Cultures in the HL treatment entered stationary phase four days post‐treatment and rapidly declined while control cultures entered and maintained stationary phase two days later. There were no differences in expression of KB2006 or KB5299 between the control and HL cultures at the transcript level analyzed by qPCR. At the protein level analyzed by western blotting, KB2006 was approximately four times more abundant in HL cultures than control cultures, and KB5299 was half as abundant in HL conditions compared to control at T6. High light intensity affects growth and protein abundance of PKS proteins in the non‐toxic sub‐strain of K. brevis providing additional evidence linking chloroplast physiology and toxicity. Additional analyses are underway to examine effects of HL on brevetoxin production. Developing a better understanding of biosynthetic pathways involved in brevetoxin production will play a pivotal role in management of future algal blooms.