White-petal California poppy varieties show reduced flower PSY transcript. (a) Left, Carotenoid biosynthetic pathway, with pigment colors approximated by colored text. Abbreviations: GGPP, geranylgeranyl diphosphate; PSY, phytoene synthase; PDS, phytoene desaturase; ZDS, ζ-carotene desaturase; CRTISO, carotenoid isomerase; LCYE, lycopene ε-cyclase; LCYB, lycopene β-cyclase; CHYB, carotene β-hydroxylase; ZEP, zeaxanthin epoxidase. Right, heatmap depicts flower bud transcript levels of the major carotenoid biosynthetic pathway genes, normalized to housekeeping gene EIF4A2. Note, only phytoene synthase (PSY) transcript levels are significantly altered in white-petal varieties, which show on average 2.5-fold reduction (P = 0.003). (b) Representative California poppy varieties studied (clockwise from top left): single white poppy in a field of golden poppies; Orange; California Golden; Golden West; White; Alba; White Linen; and Ivory Castle.