Manipulation of ZDS in Tomato Exposes Carotenoid- and ABA-Specific Effects on Fruit Development and Ripening.

Spontaneous mutations in fruit-specific carotenoid biosynthetic genes of tomato (Solanum lycopersicum) have led to improved understanding of ripening-associated carotenogenesis. Here we confirm that ZDS is encoded by a single gene in tomato transcriptionally regulated by ripening transcription factors RIN, NOR, and ethylene. Manipulation of ZDS was achieved through transgenic repression and heterologous over-expression in tomato. CaMV 35S driven RNAi repression inhibited carotenoid biosynthesis in all aerial tissues examined resulting in elevated levels of ζ-carotene isomers and upstream carotenoids, while downstream all trans-lycopene and subsequent photoprotective carotenes and xanthophylls were diminished. Consequently, immature fruit displayed photobleaching consistent with reduced levels of the photoprotective carotenes and developmental phenotypes related to a reduction in the carotenoid-derived phytohormone abscisic acid (ABA). ZDS repressed ripe fruit were devoid of the characteristic red carotenoid, all trans-lycopene, and displayed brilliant yellow pigmentation due to elevated 9,9' di-cis-ζ-carotene. Over-expression of the Arabidopsis thaliana ZDS (AtZDS) gene bypassed endogenous co-suppression and revealed ZDS as an additional bottleneck in ripening-associated carotenogenesis of tomato. Quantitation of carotenoids in addition to multiple ripening parameters in ZDS altered lines and ABA-deficient fruit-specific carotenoid mutants was used to separate phenotypic consequences of ABA from other effects of ZDS manipulation and reveal a unique and dynamic ζ-carotene isomer profile in ripe fruit.