Carotenoids have various roles in plant physiology. Plant carotenoids are synthesized in plastids and are highly abundant in the chromoplasts of ripening fleshy fruits. Considerable research efforts have been devoted to elucidating mechanisms that regulate carotenoid biosynthesis, yet, little is known about the mechanism that triggers storage capacity, mainly through chromoplast differentiation. The Orange gene (OR) product stabilizes phytoene synthase protein (PSY) and triggers chromoplast differentiation. OR underlies carotenoid accumulation in orange cauliflower and melon. The OR’s ‘golden SNP’, found in melon, alters the highly evolutionary conserved Arginine108 to Histidine and controls β-carotene accumulation in melon fruit, in a mechanism yet to be elucidated. We have recently shown that similar carotenogenic metabolic flux is active in non-orange and orange melon fruit. This flux probably leads to carotenoid turnover but known carotenoid turnover products are not detected in non-orange fruit. Arrest of this metabolic flux, using chemical inhibitors or mutations, induces carotenoid accumulation and biogenesis of chromoplasts, regardless of the allelic state of OR. We suggest that the ‘golden SNP’ induces β-carotene accumulation probably by negatively affecting the capacity to synthesize downstream compounds. The accumulation of carotenoids induces chromoplast biogenesis through a metabolite-induced mechanism. Carotenogenic turnover flux can occur in non-photosynthetic tissues, which do not accumulate carotenoids. Arrest of this flux by the ‘golden SNP’ or other flux-arrest mutations is a potential tool for the biofortification of agricultural products with carotenoids.
Bibliographical noteFunding Information:
This research was partially supported by BARD, the United States Israel Binational Agricultural Research and Development Fund, Award No. US-4918-16CR and by the ARO’s Center for the Genetic Enhancement of Cucurbit Fruit Quality. We thank Carly Golodets and Harry S. Paris for English language editing.
© Copyright © 2019 Feder, Chayut, Gur, Freiman, Tzuri, Meir, Saar, Ohali, Baumkoler, Gal-On, Shnaider, Wolf, Katzir, Schaffer, Burger, Li and Tadmor.
- OR genes
- carotenoids accumulation
- melon (Cucumis melo L.)
- metabolic flux
- tomato (Solanum lycopersicum)
ASJC Scopus subject areas
- Plant Science