Developmental control and biotechnology of floral pigmentation

Extract

[...] Floral pigmentation is under strict developmental control and is commonly linked to fertility status. The developmental signalling involved can be complex, as more than one pigment pathway, and other pathways regulating other components that affect color like vacuolar pH, may be coordinately controlled. SUMMARY This text reviews the knowledge on the regulation of pigment production during flower development, with an emphasis on the transcriptional regulation of the biosynthetic genes. It also provides a brief overview of the major flower pigment biosynthetic pathways. [...]

[...] Furthermore, esterification is a common characteristic of floral carotenoids, and may aid in the accumulation of the high levels of pigment found in chromoplasts. Pigments derived from carotenoid catabolism The vividly colored apocarotenoids are formed by cleavage of the normal C40 carotenoid structure. They occur in various plant tissues including roots, stems and flowers. Saffron, an expensive spice made from the dried red styles of saffron flowers, derives its distinctive color from C20 apocarotenoid crocetin glycosides. These are probably formed by cleavage of zeaxanthin by zeaxanthin 8(7', 8')-cleavage dioxygenase, a plastid- localized enzyme that removes the cyclic rings from both ends. [...]

[...] The chain elongation that is required to form phytoene begins with the condensation of IPP and DMAPP to form the C10 compound geranyl pyrophospate (GPP). Further sequential additions of IPP yield the C20 molecule geranylgeranyl pyrophosphate (GGPP). The conversion of IPP/ DMAPP to GGPP is catalysed by GGPP synthase (GGPPS). The subsequent formation of phytoene (in the 15-cis isomer form) is through a two-step process involving the condensation of two molecules of GGPP by phytoene synthase (PSY). Formation of carotene pigments A series of desaturation, isomerization and cyclization reactions form a variety of other carotenes from phytoene. [...]

[...] In the formation of the rare deoxyanthocyanins, which give orange and red floral colours, a variant of DFR (initially referred to as flavanone 4-reductase or FNR) is capable of reducing flavanone substrates to flavan-4-ols (3-deoxyleucoanthocyanidins). Formation of anthocyanins The first anthocyanin formed in most plants is an anthocyanidin glycoside. It is formed from leucoanthocyanidin through the activity of anthocyanidin synthase (ANS, also referred to as leucoanthocyanidin dioxygenase) and an anthocyanidin 3-O-glycosyltransferase (3GT). The ANS product is an anthocyanidin in a colorless pseudobase form, which serves as the substrate for a 3GT. [...]

[...] Malonyl- CoA and CoA esters of HCAs can also feed into the flavonoid pathway at later stages as acid group donors in the acylation of the end products. Formation of chalcones and aurones The first step committed to flavonoid synthesis is the formation of chalcone pigment, which establishes the C15 flavonoid structure. Chalcone synthase (CHS) is the enzyme involved. Naringenin chalcone is the first flavonoid formed in most plants, through the use of the HCA-CoA substrate coumaroyl-CoA. To function as floral pigments, naringenin chalcone, or chalcones derived from it, must be stabilized to prevent spontaneous conversion to colorless flavanone isomers. [...]