Abstract
Although yellow and orange petal colors are derived from carotenoids in many plant species, this has not yet been demonstrated for the order Caryophyllales, which includes carnations. Here, we identified a carnation cultivar with pale yellow flowers that accumulated carotenoids in petals. Additionally, some xanthophyll compounds were esterified, as is the case for yellow flowers in other plant species. Ultrastructural analysis showed that chromoplasts with numerous plastoglobules, in which flower-specific carotenoids accumulate, were present in the pale yellow petals. RNA-seq and RT-qPCR analyses indicated that the expression levels of genes for carotenoid biosynthesis and esterification in pale yellow and pink petals (that accumulate small amounts of carotenoids) were similar or lower than in green petals (that accumulate substantial amounts of carotenoids) and white petals (that accumulate extremely low levels of carotenoids). Pale yellow and pink petals had a considerably lower level of expression of genes for carotenoid degradation than white petals, suggesting that reduced degradation activity caused accumulation of carotenoids. Our results indicate that some carnation cultivars can synthesize and accumulate esterified carotenoids. By manipulating the rate of biosynthesis and esterification of carotenoids in these cultivars, it should be feasible to produce novel carnation cultivars with vivid yellow flowers.
Highlights
Flower coloration is an important aspect of the quality of ornamental plants
In marigolds (Tagetes erecta), the high accumulation of total carotenoids in deep yellow petals is the result of a relatively high level of expression of the deoxyxylulose 5-phosphate synthase (DXS) and phytoene synthase (PSY) genes compared to expression levels in pale yellow p etals[17]
In chrysanthemum (Chrysanthemum morifolium), lily (Lilium brownii), crocus (Crocus sativus), the cultivated brassica species, and petunia (Petunia × hybrida), all of the carotenogenic genes are expressed during carotenoid synthesis; synthesized carotenoids are rapidly degraded by the high levels of the carotenoid cleavage dioxygenase 4 (CCD4) enzyme, leading to white petals[22,23,24,25,26]
Summary
The major pigments in plants that determine flower color are flavonoids (including anthocyanins), carotenoids, betalains, and chlorophylls. Red and yellow colors in most plant species are produced by flavonoids, anthocyanins, and carotenoids. Carotenoids are fat soluble pigments and are present in a wide range of plant species and produce yellow and orange coloring. In a survey of the relationship between flower colors and flavonoid compositions of carnation petals, we found that the cultivar ‘Club’, which has pale yellow flowers, did not have detectable levels of chalcone derivatives. To determine the mechanism of carotenoid accumulation in ‘Club’ petals, we compared carotenoid compositions in four carnation cultivars and analyzed their patterns of expression of genes for enzymes involved in pigment metabolism
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