Cloning of tangerine from Tomato Reveals a Carotenoid Isomerase Essential for the Production of β-Carotene and Xanthophylls in Plants

Abstract

Carotenoid biosynthesis in plants has been described at the molecular level for most of the biochemical steps in the pathway. However, the cis-trans isomerization of carotenoids, which is known to occur in vivo, has remained a mystery since its discovery five decades ago. To elucidate the molecular mechanism of carotenoid isomerization, we have taken a genetic map-based approach to clone the tangerine locus from tomato. Fruit of tangerine are orange and accumulate prolycopene (7Z,9Z,7 Z,9 Z-tetra-cis -lycopene) instead of the all-trans -lycopene, which normally is synthesized in the wild type. Our data indicate that the tangerine gene, designated CRTISO , encodes an authentic carotenoid isomerase that is required during carotenoid desaturation. CRTISO is a redox-type enzyme structurally related to the bacterial-type phytoene desaturase CRTI. Two alleles of tangerine have been investigated. In tangerine mic , loss of function is attributable to a deletion mutation in CRTISO , and in tangerine 3183 , expression of this gene is impaired. CRTISO from tomato is expressed in all green tissues but is upregulated during fruit ripening and in flowers. The function of carotene isomerase in plants presumably is to enable carotenoid biosynthesis to occur in the dark and in nonphotosynthetic tissues.

Carotenoids in nature: insights from plants and beyond

“…phytoene, phytofluene, z-carotene and neurosporene in addition to prolycopene) instead of the typical xanthophyll profile in nonphotosynthetic tissues such as flowers (e.g. petals), the inner pericarp of green fruit and etiolated seedlings (Isaacson et al 2002;Park et al 2002). The function of these cis-carotenoids remains largely unknown and it is easy to speculate that they could play a role as novel signalling molecules.…”

“…Despite the block from cis-to an all-trans-configuration in crtiso mutants, carotenogenesis can proceed in chloroplasts via photoisomerisation, but there is a delay in the greening of etiolated seedlings and a substantial reduction in lutein in Arabidopsis as well as some degree of chlorosis in tomato and rice (Isaacson et al 2002;Park et al 2002;Fang et al 2008;Wei et al 2010;Chai et al 2011). Perhaps, CRTISO plays important roles in non-green tissues (e.g.…”

“…Perhaps, CRTISO plays important roles in non-green tissues (e.g. fruit and root appear to be protected from photoisomerisation) and in germinating seeds as they grow through the soil towards the light (Isaacson et al 2002;Park et al 2002). The role of light in substituting for the absence of CRTISO activity in green tissues is under debate and now emerges as an exciting area of intense carotenoid research to unravel the elusive chemical mechanisms and regulatory nature associated with photoisomerisation ( Fig.…”

Golden Rice – five years on the road – five years to go?

“…The bacterial CRTI transgene in particular was suspected to be the cause of this phenomenon because this desaturase differs from the plant-type desaturases, not only structurally but also in the nature of the lycopene produced: all-trans in the bacterial system but specifically poly-cis when produced by plant-type carotene desaturases (Figure 2) [15]. In plants, this requires an additional enzyme, the recently identified carotene cis-trans-isomerase (CRTISO) [16,17], to enable cyclization and the production of all-trans b-carotene. The artificial accumulation of all-trans lycopene in daffodil flowers by the application of the cyclase inhibitor CPTA [2-(p-chlorophenylthio)triethylammonium chloride] led to altered expression levels of carotenogenic mRNAs and seemingly underscored the relevance of such a feedback mechanism [18].…”

Obtenção e uso de linhagens quase isogênicas de tomateiro (Solanum lycopersicum L. cv Micro-Tom) afetando a composição de carotenoides: uma ferramenta para o estudo da nutracêutica

“…As insaturações permitem a isomeria cis-trans das moléculas; sendo que em plantas superiores ocorre a predominância dos isômeros trans (ISAACSON, 2002).…”