The role of diatom glucose-6-phosphate dehydrogenase on lipogenic NADPH supply in green microalgae through plastidial oxidative pentose phosphate pathway.

Commercial production of biofuel from oleaginous microalgae is often impeded by their slow growth rate than other fast-growing algal species. A promising strategy is to genetically engineer the fast-growing algae to accumulate lipids by expressing key lipogenic genes from oleaginous microalgae. However, lacking of strong expression cassette to transform most of the algal species and potential metabolic target to engineer lipid metabolism has hindered its biotechnological applications. In this study, we engineered the oxidative pentose phosphate pathway (PPP) of green microalga Chlorella pyrenoidosa for lipid enhancement by expressing a glucose-6-phosphate dehydrogenase (G6PD) from oleaginous diatom Phaeodactylum tricornutum. Molecular characterization of transformed lines revealed that heterologous PtG6PD was transcribed and expressed successfully. Interestingly, subcellular localization analyses revealed that PtG6PD was targeted to chloroplasts of C. pyrenoidosa. PtG6PD expression remarkably elevated NADPH content and consequently enhanced the lipid content without affecting growth rate. Collectively, this report represents a promising candidate to engineer lipid biosynthesis in heterologous hosts with notable commercial significance, and it highlights the potential role of plastidial PPP in supplying lipogenic NADPH in microalgae.