Methylation pattern and expression dynamics of methylase and photosystem genes under varied light intensities in Fugacium kawagutii (Symbiodiniaceae).

Previous studies have indicated extensive methylation of CpG islands and abundant methyltransferase gene (DNMT) in Fugacium kawagutii (formerly Symbiodinium kawagutii) genome. However, whether DNA methylation plays a role in regulating gene expression in this and other dinoflagellates remains unclear. Here we characterized gene body methylation levels using methylation-specific PCR (MS-PCR) and bisulfide sequencing PCR (BSP) and measured transcriptional levels for three photosystem genes in F. kawagutii under different light conditions (20, 100 and 600 µE · m-2 · s-1 ). To explore the association of methylation with DNA methylase, the expression of DNA methyltransferase (Symbio-DIRS-Dnmt3) was also measured. Our results showed that peridinin-chlorophyll a binding protein (PCP), light harvesting complex (LHC) and chlorophyll a-c binding protein complex (acpPC) gene expression was all significantly up-regulated under low light in which their methylation level was down-regulated, constant and elevated, respectively. Symbio-DIRS-Dnmt3 exhibited elevated transcriptional level under increased light intensity. The results led us to hypothesize that DNA methylation level can be modulated by environmental conditions such as irradiance, probably through the regulation of Symbio-DIRS-Dnmt3 transcription level, and in turn may regulate the expression of genes in F. kawagutii. Further study is needed to determine whether the same gene methylation and expression characteristics reported here occur in other dinoflagellates and to explore their ecological implications.