Engineering Saccharomyces cerevisiae to improve heterologous abscisic acid production

Journal article, 2026

Background Abscisic acid (ABA) is a phytohormone involved in regulating plant growth, development, and stress responses. Its various physiological activities in plants and animals make the molecule a high-value product with agricultural, medical and nutritional applications. We previously constructed an ABA cell factory by expressing the ABA metabolic pathway from Botrytis cinerea in the biotechnological workhorse Saccharomyces cerevisiae. In this study, we aimed to improve ABA production and explored various rational engineering targets mostly focusing on increasing the activity of the two cytochrome P450 monooxygenases of the ABA pathway, BcABA1 and BcABA2. We evaluated the effects of cell membrane transporters, expression of heterologous cytochrome b5, improving heme supply, altering ER homeostasis, expression of Arabidopsis thaliana proteins and improving the precursor supply. Results One of the genes involved in ER membrane homeostasis, PAH1, was identified as a promising engineering target. Knock-out of PAH1 improved ABA titers but also caused a severe growth defect. By replacing the PAH1 promoter with a weak minimal promoter, it was possible to mediate the growth defect while still improving ABA production. However, we also found that, in terms of ABA titer, a strain expressing the A. thaliana genes encoding the membrane steroid binding protein 1 (AtMSBP1) and the putative transcription factor CONSTANS-like 4 protein (AtCOL4) outperformed a highly-engineered strain with two copies of bcaba1 and bcaba2, PAH1 knockdown and further genetic modifications. Solely overexpressing the two plant proteins increased ABA titers by more than fivefold. Conclusions In this report we were able to improve ABA titers and furthermore provide valuable insights for engineering other cell factories containing cytochrome P450 monooxygenases. Our results demonstrate that expressing heterologous plant proteins can be a simple yet highly effective engineering strategy to increase P450 monooxygenase activity.