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Regulation of pigment biosynthesis in flowers

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  1. Introduction.
  2. Regulation of pigment biosynthesis in flowers.
    1. The induction of the pigment biosynthetic genes.
    2. Adequate carbohydrate level.
    3. Post-transcriptional regulation.
    4. Post-transcriptional translational mechanisms.
  3. Regulation of flavonoid production in flowers.
    1. Regulation of the production of flavonoid precursors.
    2. TFs regulating anthocyanin production.
    3. Regulation of the production of other floral flavonoid pigments/co-pigments.
  4. Genetic modification of flower pigmentation.
  5. Flavonoids.
  6. Carotenoids.
  7. Betalains.
  8. Conclusion.

Flower color, along with fragrance, floral shape and nectar reward, is important to the interaction between plants and pollinators; and preferences towards specific colors are exhibited by pollinators, whether they are birds, bees, butterflies or other insects. Commonly contributing to floral phenotypes are color combinations and patterning such as distinctive spots on the flower ?lip' or pigment lines in the flower tube. These may provide more specific signals within the flower, e.g. acting as nectar guides to insects. In an extraordinary example of pollinator signaling, the flowers of the orchid genus Ophrys use color, scent and shape to mimic female bees, causing the male bee to attempt copulation, thus achieving pollination. The major pigments responsible for flower color are carotenoids, flavonoids and betalains. Although other pigment types such as chlorophylls, phenylphenalenones and quinochalcones can generate flower colors, their occurrence is rare. Carotenoids are lipid soluble, plastid-located terpenoids present in photosynthetic plants, algae and bacteria. For pigmentation of flowers (and fruits), carotenoids accumulate to high levels in specialized plastids called chromoplasts. These pigments participate in the harvesting and dissipation of light energy in chloroplasts, protecting the photosynthetic machinery from photo-oxidation.

[...] Flavonoids There are numerous examples of modification of flavonoid biosynthesis in flowers of transgenic plants. There are also several examples for grains, fruit and vegetable crops. The major methods are based on manipulation of pathway flux. The approaches to increasing, preventing or redirecting flux into or within the pathway have used up- or downregulation of the pathway using regulatory factors; introducing new biosynthetic activities; increasing specific endogenous biosynthetic activities; and abolishing branches of the pathway. The latter may cause substrate to accumulate or be directed into alternative biosynthetic branches. [...]

[...] For anthocyanin synthesis, it has been shown that major increases in transcript abundance for the biosynthetic genes precede pigment production, and that this is due to increased transcription of the genes. There are few studies for flowers pigmented by carotenoids or betalains. However, recent studies have shown that increases in transcript abundance occur for several carotenoid biosynthetic genes concomitant with flower coloration in daffodil. Similarly, transcript abundance for the betalain biosynthetic enzyme DOD correlates with pigmentation in flowers of P. [...]

[...] In particular, removal of the anthers will prevent normal anthocyanin pigment formation in flowers of petunia and Viola cornuta. In V. cornuta, the open flowers change from white to purple only when they are both exposed to light and pollinated, with pollination triggering specific changes in anthocyanin biosynthetic gene expression. In petunia, it is thought that anther-produced gibberellic acid is a developmental signal translocated to the corolla to modulate petal growth and induce anthocyanin pigmentation. GA1 and GA4 have been identified in petunia anthers and corollas, and exogenous GA1, GA3 or GA4 will compensate for anther excision and promote gene transcription for several anthocyanin biosynthetic enzymes. [...]

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