www.checkbiotech.org ; www.raupp.info ; www.czu.cz

Forget roses; when it comes to investigating the foundations of floral
fragrance, petunias are the blossom of choice for Dutch researchers, March
2006 by Laura Durnford.

Their discovery of a genetic 'master-switch' that controls scent synthesis
could lead to interesting developments for scientists, gardeners and
commercial growers alike.

Trumpet-like flowers in all shades of pink and white adorn the various types
of petunias which grow in the complex of greenhouses run by the University
of Amsterdam's Plant Physiology department.

The differences in size, shape and hairiness of these plants reflect the
genetic diversity collected together here.

According to Julian Verdonk, who recently completed a PhD here, petunias
naturally produce a large number of mutant forms, and it's this genetic
variability as well as their large and fragrant flowers which makes them
ideal subjects for research into the genetic underpinnings of blossom and
scent production.

Petunia pathway

"We are interested in petunias because they produce a lot of scent in a
certain chemical family," explains Dr Verdonk. These volatile aromatic
chemicals are known to be important not only for the final fragrance of a
flower, but also for the flavour of fruits and for the way in which plants
signal to insects.

Also, since the petunia is related to commercial crops such as potatoes and
tomatoes, the potential to manipulate these characteristics could be of
great interest.

"If we have certain information about the pathway of synthesis of these
compounds in petunias, we can maybe implement this in research on the
flavour of tomatoes or other commercial species," Dr Verdonk confirms.

Biological rhythm

The scientists have certainly scented success in their studies. The first
step was to trap the volatile compounds emitted by the flowers, using a
glass funnel and a carefully positioned needle that siphoned the aromas into
equipment to analyse the chemicals involved.

Twelve different types of aromatic 'benzenoid' molecules were identified,
"and I discovered that the flower has a rhythm in its scent emission," adds
Dr Verdonk. "It has a 24 hour cycle with the maximum in the night."

Given that petunias are pollinated by night-flying moths, this pattern of
scent synthesis is not surprising. But the fact that the genes responsible
for producing scent are only actively 'expressed' at certain times gave Dr
Verdonk a useful insight. By examining the pattern of gene expression in
petunia petals at different times of day, "I found a lot of genes from the
pathway" which leads to scent production, "but the most interesting
candidate was a certain transcription factor, like a 'switch', which can
turn on the expression of a lot of genes at the same time."

Masterswitch

When the researchers checked whether this gene's expression coincided with
scent production, "we found it did". So, fairly sure they were on the right
track, they named it 'ODORANT 1', before seeking final confirmation that it
was indeed the master-switch. "By genetic manipulation of the whole plant, I
made 'lines' where the expression of this gene was lower, or off in certain
cases," Dr Verdonk explains. "The plants lost their scent. So this was the
last evidence we needed that this was indeed a very important gene."

Nighttime pollination by a moth

Dr Verdonk foresees various avenues for further research on 'ODO 1', as it
has become known. The fact that the gene follows a 24 hour cycle of
expression could make it of interest for scientists investigating how
biological rhythms and 'body clocks' are regulated. He says commercial
growers could benefit if the scents which attract specific insects could be
tweaked to improve pollination rates in greenhouses, or if less appetising
flavours could be eliminated from crops such as tomatoes.

The ability to improve fragrance in many of the showiest types of flowers
could make gardeners happy.

Scent manipulation

According to Dr Verdonk, it should be possible to achieve all this without
having to develop transgenic plants - which would be problematic in Europe.
Instead classic breeding techniques could simply be speeded up, using ODO 1
as a 'marker' for the requisite characteristics, without the traditional
element of 'trial and error' in what results.

"Using this knowledge we have now, we could really start to manipulate not
only the scent of commercial flowers, but also taste and colour; the
connection of ODORANT 1 with all these different pathways makes it a very
interesting candidate."

[www.radionetherlands.nl]

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