Environmental and nuclear influences on microalgal chloroplast gene expression

Microalgal chloroplasts, such as those of the model organism Chlamydomonas reinhardtii, are emerging as a new platform to produce recombinant proteins, including industrial enzymes, diagnostics, as well as animal and human therapeutics. Improving transgene expression and final recombinant protein yields, at laboratory and industrial scales, require optimization of both environmental and cellular factors. Most studies on C. reinhardtii have focused on optimization of cellular factors. Here, we review the regulatory influences of environmental factors, including light (cycle time, intensity, and quality), carbon source (CO₂ and organic), and temperature. In particular, we summarize their influence via the redox state, cis-elements, and trans-factors on biomass and recombinant protein production to support the advancement of emerging large-scale light-driven biotechnology applications.