Fig. 1

Overview of the multimodular strategy for betulinic acid-related triterpenoid production in Y. lipolytica. All the genes that were engineered in this study are presented, and the betulinic acid biosynthesis pathway was divided into four modules: the red arrow represents the heterogenous CYP/CPR module (CYP is lupeol C-28 oxidase and CPR is NADPH-cytochrome P450 reductase. Both originate from the five sources). The yellow arrow represents the MVA module with 3 genes (ERG1/ERG9/HMG1) that are overexpressed separately or simultaneously. The green arrow represents the redox cofactor supply module with four introduced genes, namely, EMC, EMT, Rtme (encoding malic enzyme, which is responsible for NADPH generation) and Gapc (encoding glyceraldehyde-3-phosphate dehydrogenase, which is responsible for NADH generation). The blue arrow represents the acetyl-CoA generation module with seven endogenous genes overexpressed (ACL1 and ACL2, encoding ATP citrate lyase, which can directly increase acetyl-CoA levels; PXA1, MFE1, PEX10, POT1 and TGL3 in the β-oxidation pathway, which are responsible for the catabolism of fatty acids to generate acetyl-CoA)