Elucidation of the Pathway to Astaxanthin in the Flowers of Adonis aestivalis    

Abstract

A few species in the genus Adonis are the only land plants known to produce the valuable red ketocarotenoid astaxanthin in abundance. Here, we ascertain the pathway that leads from the b-rings of b-carotene, a carotenoid ubiquitous in plants, to the 3-hydroxy-4-keto-b-rings of astaxanthin (3,39-dihydroxy-b,b-carotene-4,4'-dione) in the blood-red flowers of Adonis aestivalis, an ornamental and medicinal plant commonly known as summer pheasant's eye. Two gene products were found to catalyze three distinct reactions, with the first and third reactions of the pathway catalyzed by the same enzyme. The pathway commences with the activation of the number 4 carbon of a b-ring in a reaction catalyzed by a carotenoid b-ring 4-dehydrogenase (CBFD), continues with the further dehydrogenation of this carbon to yield a carbonyl in a reaction catalyzed by a carotenoid 4-hydroxy-b-ring 4-dehydrogenase, and concludes with the addition of an hydroxyl group at the number 3 carbon in a reaction catalyzed by the erstwhile CBFD enzyme. The A. aestivalis pathway is both portable and robust, functioning efficiently in a simple bacterial host. Our elucidation of the pathway to astaxanthin in A. aestivalis provides enabling technology for development of a biological production process and reveals the evolutionary origin of this unusual plant pathway, one unrelated to and distinctly different from those used by bacteria, green algae, and fungi to synthesize astaxanthin.

Astaxanthin and Related Xanthophylls

“…It has been suggested that in Adonis plants, the synthesis of a 3-hydroxy-4-keto-β(beta)-ionone ring from the β(beta)-ionone ring substrate is controlled by two genes and occurs in three steps [ 99 ]. First, a 4-hydroxy-β(beta)-ring is formed by carotenoid-β(beta)-ring-4-dehydrogenase (CBFD); second, 4-hydroxy-β(beta)-ring-4-dehydrogenase (HBFD) continues with the further dehydrogenation of carbon 4 giving a keto group at this position; and third, CBFD introduces a hydroxyl group at carbon 3 of the 4-keto-β(beta)-ring to form the 3-hydroxy-4-keto-β(beta)-ring.…”

Lycopene cyclase paralog CruP protects against reactive oxygen species in oxygenic photosynthetic organisms

“…5E) suggested that this compound had fewer conjugated double bonds than β-carotene. A study of the literature for rare carotenoids found in plants provided many possibilities (21)(22)(23)(24), but none seemed more likely than β-carotene-5,6-epoxide, a carotenoid that has previously been observed in photosynthetic tissues (21). β-carotene-5,6-epoxide was synthesized (25) and subjected to HPLC analysis, where it eluted at the same time and with the same spectrum as the unknown carotenoid ( Fig.…”

Engineering of tomato for the sustainable production of ketocarotenoids and its evaluation in aquaculture feed

“…The high β-carotene line used in this study (RI) derives from the crossing of the cultivated tomato S. lycopersicum [LA4024 in the Tomato Genetics Resource Center (TGRC) database] with the wild S. galapagense accession (LA0483 in the TGRC database) (12,13). Two ZW events (10)(11)(12)(10)(11)(12)(13)(14)(15)(16)(17) were crossed with two RI lines (RI33 and RI1). The lines were cross-pollinated.…”

“…However, on a production cost-basis, a plant-based source remains the most economically viable (8,9). The only plant capable of ketocarotenoid (astaxanthin/phoenicoxanthin) formation is Adonis aestivalis, which is not amenable to agricultural production and contains toxic alkaloids (10,11). Thus, a genetic engineering approach of an agricultural crop offers a viable alternative.…”