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Flower colour and cytochromes P450
Yoshikazu Tanaka and Filippa Brugliera
Philosophical Transactions of the Royal Society B
2. Seminar Biotechnologie Viola Schweitzer, SS14
Introduction
Role of cytochromes P450 in flower colours
- evolution
- F3'5'H (CYP75A), F3'H (CYP75B)
Efforts to blue
Efforts to red
Future callenges
Introduction
The colour of flowers depends on the pigments present in the vacuole. This could be flavonoids,
carotenoids or betalains, of which flavonoids are the most colourful pigments. Anthocyanins are
flavonoids that range from yellow, orange and red colours to blue ones and also colours invisible to
the human eye. These are improtant insect attractants.
Factors that influence the colour are the structure of anthocyanins, the pH value in the vacuole as
well as co-pigments and metal ions.
Fig. 1: Visible light spectrum
Anthocyanins
The
pathway
of
the
anthocyanin
production
ist
very
phosphoenolpyruvate, which is then converted to phenylalanine.
Fig. 2: Anthoycyanine pathway I
abundant,
the
precursor
is
Cyanidin, pelargonidin and delphinidin are the first colourful products of the pathway.
Fig. 3: Anthoycyanine pathway II
The pigments were named after the flowers they were first isolated from.
Fig. 4: Flowers the pigments were isolated from
Role of cytochromes P450 in flower colours
The pathway to anthocyanins is generally conserved in flowering plants. The most important
enzymes are the flavonoid-3'-5'- and flavonoid-3'-hydroxylases, which catalyze hydroxylations of
B-ring.
If there is a lack of F3'5'H, the flowers usually don't show blue colours.
Fig. 5: Flavonoid structure
Evolution
The first purpose of petal colours was the attraction of pollinators as a reproductional strategy.
The F3'H (CYP75B) and F3'5'H (CYP75A) belong to CYP71 clan, a family of CYP450 enzymes.
Another important enzyme is the flavone synthase II (CYP93B family), which is involved in the copigment synthesis.
Fig. 6: Plant-pollinator interaction
Fig. 7: Evolutionary tree of CYP75B and CYP75A
Evolutionary research has lead to some interesting results concerning flower colours. One is that
blue was probably the original flower colour, considering the change from blue to red was observed
more often than fromred to blue. Also, red colours often occured due to mutations of the F3'5'H
(loss of function). Sometimes, blue colours reoccured due to the neofunctionalization of the
CYP75B gene.
Fig. 8: Duplication of the F3'5'H in wine
F3'5'H (CYP75A), F3'H (CYP75B)
Blue is the most desired petal colour, especially for roses.
Fig. 9: "Blue" pathway
Unfortunately, the top selling cut flowers (rose, carnation, lilly, chrysanthemum) are F3'5'H
deficient.
The modification of F3'5'H and F3'H is an approach for plant engineering.
Fig. 10: "Red" pathway
Efforts to blue
I) isolation of tool genes (F3'5'H, FSNII)
II) efficient transformation system
III) optimization of transgene expression
IV) selection of host cultivars (appropriate genetic background)
The strategies include the overexpression of exogenous genes, the downregulation of competing
pathways or working on mutant lines lacking those.
Possible plant promotors are the CaMV 35S, Mas -> Mac.
For example, carnations are usually pale yellow, pink or white.
The general flavone pathway intact, so the heterogenous expression of petunia F3'5'H (snapdragon
promotor region) and petunia DFR (Mac-1 promotor) was successful as it lead to the first violet
carnations.
Fig. 11: Modified carnations
Roses are more difficult, as they have hardly any flavone production and a low vacuolar pH value.
Also, heterogenous F3'5'H transcripts are unstable and even large amounts of delphinidin do not
result in pure blue colours.
For a darker red, the pansy F3'5'H under a CaMV 35S promotor was applied.
Fig. 12: Modified roses
Efforts to red
These strategies are used to change blue or violet to red, and also intensifying a pale red.
Pale petals are due to abscence of pelargonidin, the main causes are the substrate specificy of the
DFR or a dominant F3'H activity.
Because of the side effects of this manipulations, elaborate strategies are required.
Difficulties
- vacuolar pH value: ATP-dependent process, disturbances may be fatal
- metal ions: colourful complexes, interfere with pigment colours, potentially toxic effects
Fig. 13: Metal ion complex colours
- co-pigments: colour of second-rank, difficult to predict consequences of manipulation
- pathway redirection: shortage of early precursors (odourant substances, mediators)
Torenia & Gentian
The results of approaches to turn petals red are far behind the efforts to blue.
I) knock-out of F3'5'H
II) careful modification of other factors
Fig. 14: Modified torenia
Future challenges
The accumulation of P450 generated pigments only is not straight forward, as the influence of
F3'5'H and F3'H on petal colour is comparatively slight considering all plant processes.
Also, extensive manipulation of conditions and pathways may cause a loss of plant vitality.
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