Initial evidence of functional siRNA machinery in dinoflagellates

Dinoflagellates are a major group of protists widely distributed in the aquatic environments. Many species in this lineage are able to form harmful algal blooms (HAB), some even producing toxins, making this phylum the most important contributors of HAB in the marine ecosystem. Despite the ecological importance, the molecular mechanisms underpinning the basic biology and HAB formation of dinoflagellates are poorly understood. While the high-throughput sequencing studies have documented a large and growing number of genes in dinoflagellates, their functions remained to be experimentally proven using a functional genetic tool. Unfortunately, no such tool is yet available. This study was aimed to adopt the RNA interference (RNAi) gene-silencing tool for dinoflagellate research, and to investigate the potential effects of RNAi-based silencing of proton-pump rhodopsin and CO₂-fixing enzyme Rubisco encoding genes in dinoflagellates. It was found that RNAi treatment caused a significant decrease in growth rate in both species. Compared with the non- endogenous target (GFP-siRNA) and the blank control, RNAi treatments also suppressed the expression of the target genes. These results constitute the first experimental evidence of the existence and operation of siRNA in two species of dinoflagellates, present initial evidence that dinoflagellate rhodopsins are functional as a supplemental energy acquisition mechanism, and provide technical information for future functional genetic research on dinoflagellates.