METABOLISM OF CYCLIC CAROTENOIDS - A MODEL FOR THE ALTERATION OF THISBIOSYNTHETIC-PATHWAY IN CAPSICUM-ANNUUM CHROMOPLASTS

The biosynthetic pathway of cyclic carotenoid is known to be quantitat ively and qualitatively different in the nongreen plastids of Capsicum annuum fruits compared with chloroplasts. Here, the cloning is descri bed of a novel cDNA from this organism, which encodes an enzyme cataly zing the cyclization of lycopene to beta-carotene when expressed in Es cherichia coli. The corresponding gene is constitutively expressed dur ing fruit development. Significant amino acid sequence identity was ob served between this enzyme and capsanthin/capsorubin synthase which is involved in the synthesis of the species-specific red carotenoids of C. annuum fruits. The latter enzyme was found also to possess a lycope ne beta-cyclase activity when expressed in E. coli. A model is propose d for the origin of the capsanthin/capsorubin synthase gene and the ro le of this enzyme, together with the newly cloned lycopene cyclase, in the specific re-channeling of linear carotenoids into beta-cyclic car otenoids in C. annuum ripening fruits.