摘要Microalgae are used in food and feed,and they are considered a potential feedstock for sustainably pro-duced chemicals and biofuel.However,production of microalgal-derived chemicals is not yet economically feasible.Genetic engineering could bridge the gap to industrial application and facilitate the production of novel products from microalgae.Here,we report the discovery of a novel gene expression system in the oleaginous microalga Nannochloropsis that exploits the highly efficient transcriptional activity of RNA po-lymerase I and an internal ribosome entry site for translation.We identified the nucleolus as a genomic safe harbor for Pol I transcription and used it to construct transformant strains with consistently strong trans-gene expression.The new expression system provides an outstanding tool for genetic and metabolic en-gineering of microalgae and thus will probably make substantial contributions to microalgal research.