Abstract
Microalgae are used in food and feed, and they are considered a potential feedstock for sustainably produced 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 polymerase 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 transgene expression. The new expression system provides an outstanding tool for genetic and metabolic engineering of microalgae and thus will probably make substantial contributions to microalgal research.
Highlights
Microalgae are at the interface of industrial fermentation and agriculture
We developed a novel system for gene expression in N. oceanica that relies on highly efficient polymerase I (Pol I) for transcription and on an internal ribosome entry site (IRES) element for translation
Prior studies have shown that IRESs can be used to overcome translational block of Pol I-transcribed molecules in mammalian cells, yeast, and plants (Palmer et al, 1993; Ghoshal et al, 2004; Oem et al, 2007; Wen et al, 2008; Komarova et al, 2012; Sims et al, 2019), but no previous reports exist for microalgae
Summary
Microalgae are at the interface of industrial fermentation and agriculture. Their high protein content, nutritional value, and phototrophic growth rate, together with the prospect of cultivation on non-arable land, make them a potential replacement for traditional agricultural products in food and feed, as well as platforms for the biomanufacturing of a variety of desirable products for the chemical and pharmaceutical sector (Lamminen et al, 2019; Adissin et al, 2020; Sarker et al, 2020). Microalgae naturally produce many compounds of interest, including highvalue lipids, vitamins, pigments, and sterols (Levasseur et al, 2020). The toolset currently available has shown to enable the advancement of microalgae with optimized productivities (Ajjawi et al, 2017) and reduced genome size (Wang et al, 2020)
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