New abscisic acid analogues produced via genome mining-guided heterologous expression

Abscisic acid (ABA), a pivotal phytohormone, was traditionally considered to be synthesized via the carotenoid pathway exclusively in plants. In our recent work, a dedicated ABA biosynthetic gene cluster (ablt) was discovered from the marine-derived fungus Alternaria alternata JJY-32 by genome mining. Heterologous expression of the ablt cluster in Aspergillus nidulans A1145 led to the production of two new analogues of ABA, designated as abaterpene A (1) and abaterpene B (2), along with six known sesquiterpenes. Further step-wise gene co-expression analysis demonstrated that ablt3 and ablt5 are necessary and sufficient for the production of compounds 1 and 2. The structures were determined using comprehensive 1D and 2D NMR data and assisted by ECD calculations.