Fig. 4. Cucurbitacin biosynthesis in Cucurbitaceae. (A) Cucurbaticin BGC and auxiliary genes conserved in Cucumis sativus, C. melo and Citrullus lanatus. (B) Syntenic relationships of tandem CYP and TF arrays showing species-specific genomic variations. Pseudogenes are shown as rectangles and genes disrupted by a premature stop codon are marked with an asterisk (*). Leaf- (Bl), fruit- (Bt) and root-specific (Br) TFs are indicated. Arrows with a black border indicate co-expressed genes predicted to contribute to biosynthesis of Cucurbatacins. (C) Biosynthetic pathway towards CuB, -C and -E with functionally characterised enzymes shown. Pathway intermediates are represented by black circles. The final step catalysed by the respective ACTs is preceded by an intermediate biosynthesised by a yet to be identified enzyme.