Critical light-related gene expression varies in two different strains of the dinoflagellate Karlodinium veneficum in response to the light spectrum and light intensity

Abstract

The toxic dinoflagellate Karlodinium veneficum is widely distributed in cosmopolitan estuaries and is responsible for massive fish mortality worldwide. Intraspecific biodiversity is important for the spread to various habitats, interspecific competition to dominate a population, and bloom formation and density maintenance. Strategies for light adaptation may help determine the ecological niches of different ecotypes. However, the mechanism of phenotypic biodiversity is still unclear. In this study, intraspecific differences in genetic regulatory mechanisms in response to varied light intensities and qualities were comparatively researched on two different strains isolated from coastal areas of the East China Sea, namely, GM2 and GM3. In GM2, the expression of genes in the Calvin cycle, namely, rbcL and SBPase, and a light-related gene that correlated with cellular motility, rhodopsin, were significantly inhibited under high light intensities. Thus, this strain was adapted to low light. In contrast, the gene expression levels were promoted by high light conditions in GM3. These upregulated genes in the GM3 strain probably compensated for the negative effects on the maximum quantum yields of PSII (Fv/Fm) under high light stress, which inhibited both strains, enabling GM3 to maintain a constant growth rate. Thus, this strain was adapted to high light. Compared with white light, monochromatic blue light had negative effects on Fv/Fm and the relative electron transfer rate (ETR) in both strains. Under blue light, gene expression levels of rbcL and SBPase in GM2 were inhibited; in contrast, the levels of these genes, especially rbcL, were promoted in GM3. rbcL was significantly upregulated in the blue light groups. Monochromatic red light promoted rhodopsin gene expression in the two strains in a similar manner. These intraspecific diverse responses to light play important roles in the motor characteristics, diel vertical migration, interspecific relationships and photosynthetic or phagotrophic activities of K. veneficum and can determine the population distribution, population maintenance and bloom formation.

Keywords: Intraspecific difference; Karlodinium veneficum; Photosynthetic gene expression; rhodopsin gene.