Table 1 Influence of genes supplying substrates for lipid synthesis in transgenic strains
Genes | Description | Host species | Method of intervention | Effects (relative to control) | Inferred role | Ref. |
|---|---|---|---|---|---|---|
PDK | Pyruvate dehydrogenase kinase | Phaeodactylum tricornutum | Antisense knockdown | 33–82% more neutral lipids in 2 mutants | PDK deactivates Pyruvate dehydrogenase complex (PDC). Knocking down PDK increases acetyl-CoA production from pyruvate via PDC | [101] |
NADK3 | Arabidopsis thaliana NAD(H) kinase (AtNADK3) | Chlorella pyrenoidosa | Gene overexpression | Total lipid content increased by 45.3–110.4%; NADPH content increased by 39.3–79.9% | Heterologous NADH kinase increases NADPH which drives reductive biosynthesis reactions such as FA synthesis | [72] |
ACS | E. coli Acetyl-CoA synthetase (ACS) | Schizochytrium sp. | Gene overexpression | Total lipid content increased by 6.4–11.4%; Biomass increased by 24.3–29.9% | Heterologous ACS overexpression improved utilization of acetate as a carbon resource for growth and lipid synthesis | [78] |
ACL | Mus musculus ATP:citrate lyase | Yarrowia lipolytica | Gene overexpression | Total lipid content increased by 50.6–215.1%; Citrate content decreased by 32% | Heterologous expression of ACL with a low Km value for citrate increases lipid synthesis by providing more cytosolic acetyl-CoA as substrates | [138] |
PDH E1α | E1 alpha subunit of the Pyruvate Dehydrogenase Complex | Chlamydomonas reinhardtii | Artificial microRNA knockdown | Total lipid content decreased by 25–40%; Lower chlorophyll content, lower photosynthetic yield on PSII, and lower biomass in mutants | PDC serves an essential role in the supply of carbon precursors for FA synthesis under photoautotrophy | [100] |
ME | Malic enzyme | Phaeodactylum tricornutum | Gene overexpression | 2.3- to 2.5-fold more neutral lipids in 2 mutants; growth rate unaffected | ME could increase lipid synthesis without affecting biomass accumulation by providing NADPH | [128] |
ME | Phaeodactylum tricornutum malic enzyme (PtME) | Chlorella pyrenoidosa | Gene overexpression | 2.4- to 3.2-fold more neutral lipids in 2 mutants; growth rate unaffected | Heterologous ME could increase lipid synthesis without affecting biomass accumulation by providing NADPH | [129] |
G6PDH | Glucose-6-phosphate dehydrogenase | Mortierella alpina | RNAi knockdown | Total lipid content decreased by 50%; NADPH content decreased by 40% | G6PDH is a critical component of the Oxidative Pentose Phosphate Pathway which enables efficient lipid synthesis | [66] |
ACL/ME | ATP:citrate lyase and Malic enzyme | Yarrowia lipolytica | Five gene modifications including overexpression of ME and ACL subunit 1 and subunit 2 | Total lipid content increased to 74%, a 15-fold improvement over wild type (16.8%) | ACL and ME cooperatively divert carbon precursors and reducing power towards lipid synthesis, and in conjunction with other modifications, lead to enhanced lipid accumulation | [85] |