Manipulation of Carotenoid Metabolic Flux by Lycopene Cyclization in Ripening Red Pepper (Capsicum annuum var. conoides) Fruits

摘要

Carotenoids are essential phytonutrients for the human body. Higher plants usually synthesize and accumulate carotenoids in their leaves, flowers, and fruits. Most carotenoids have either two beta-rings on both ends or beta- and epsilon-rings separately on two ends of their molecules and are synthesized from the acyclic lycopene as the precursor. Lycopene beta- and epsilon-cyclases (LCYB and LCYE, respectively) catalyze the beta- and epsilon-cyclization of lycopene, respectively, and regulate the metabolic flux from lycopene to its downstream beta,beta-branches (by LCYB alone) and beta,epsilon-branches (by LCYE and LCYB). In this study, we identified and characterized genes for two LCYBs (CaLCYB1 and CaLCYB2), one LCYE (CaLCYE1), and a capsanthin/capsorubin synthase (CaCCS1) which is also able to beta-cyclize lycopene from the red pepper (Capsicum annuum var. conoides) genome. By quantifying transcript abundances of these genes and contents of different carotenoid components in ripening fruits, we observed a correlation between the induction of both CaLCYBs and the accumulation of carotenoids of the beta,beta-branch during ripening. Although capsanthin was accumulated in ripened fruits, our quantification demonstrated a strong induction of CaCCS1 at the breaker stage, together with the simultaneous repression of CaLCYE1 and the decrease of lutein content, suggesting the involvement of CaCCS1 in competing against CaLCYE1 for synthesizing carotenoids of the beta,beta-branch. Our results provide important information for future metabolic engineering studies to manipulate carotenoid biosynthesis and accumulation in fruits.