Since white poppy petals are deficient in carotenoid pigments 11, we focused on genes of the carotenoid biosynthetic pathway. Since no poppy reference genome was available, RNAseq reads were assembled de novo into transcript contigs, which were then annotated by homology to an orthologous reference transcriptome, for which we selected another eudicot clade flowering plant, the garden tomato ( Solanum lycopersicum). RNA was isolated from developing flower buds, where pigment production was presumed ongoing. Three orange-petal poppy varieties (Orange, California Golden, and Golden West) served as controls. To investigate the genetic basis of white-petal poppy variants, we carried out transcriptome sequencing (RNAseq) of developing flower buds from four different commercial white poppy varieties displaying varied shades of white: Ivory Castle, White Linen, Alba, and White (Fig. Carotenoids serve not only as chromoplast pigments to attract pollinators and horticulturalists, but also as chloroplast accessory pigments and antioxidants crucial for photosynthesis 4. Additional proteins have been reported to modulate carotenoid biosynthesis or degradation 5, 8. Notably, California poppy petals also contain abundant retro-carotenoids ( retro-carotene triol and Eschscholzxanthin), generated from antheraxanthin and violaxanthin by as yet unknown enzymes 6, 7. Subsequent enzymatic steps that include desaturation, isomerization, cyclization, hydroxylation and epoxidation sequentially generate carotenoids that appear red (lycopene), orange (α-carotene and β-carotene), and yellow (lutein, zeaxanthin, antheraxanthin, and violaxanthin), and combinations of these pigments create the observed palette. The first committed step is the condensation of two geranylgeranyl diphosphate (GGPP) molecules to phytoene (colorless), catalyzed by phytoene synthase (PSY) (Fig. The carotenoid biosynthetic pathway in plants has been well characterized 4, 5. The golden-orange color results from carotenoid pigments 3. The golden poppy has since been inextricably linked to California pop culture, even eulogized by the novelist John Steinbeck 2. First catalogued from a Russian seafaring expedition to the San Francisco Bay in the early1800s, the golden poppy was designated the state flower of California in 1903. Native Americans valued the golden poppy as a food source. The flowers are brilliant golden-orange, instantly recognizable, and widely drawn and photographed. The California poppy ( Eschscholzia californica), also known as the golden poppy, is native to the West Coast of the United States 1, 2.
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