Polyphenols - Fruit Ripening: Physiology, Signalling and Genomics - page 174

drives the pathway towards anthocyanins.
In the absence of UFGT activity, the fl ux
may be redirected towards other fl avonoid
branches, such as the PA branch. Indeed,
reduced levels of anthocyanins induced by
downregulation of UFGT in strawberry
were accompanied by an increase in
epiafzelechin (Griesser et al. , 2008).
This section has highlighted the large
array of transcription factors regulating
fl avonoid biosynthesis in fruits. This may
appear to be redundancy but probably
refl ects the necessity of numerous genes for
the fi ne-tuning of this pathway, each
regulator having a tissue, stage, biotic and
abiotic condition-specifi c expression.

quantitatively among cultivars, making
this character a potential breeding target.
By studying polyphenols biosynthetic
pathways and the genetic factors
involved, the amount of these compounds
in the fruit can be optimized to improve
nutritional quality for human con-
sumption. Polyphenols are also involved
in plant defence against biotic and abiotic
stresses. A better understanding of the
regulation processes triggering their bio-
synthesis in response to environmental
threats will be of great help for selection
(based on genetic markers) and/or
bioengineering of fruit crops showing
increased UV, heat or drought tolerance
and resistance to pathogens. The in-
creasing number of genome sequences
available for agronomical plants will
enable investigation of these complex and
challenging pathways. However, this will
also require the development of analytical
methods for high-throughput phenotyping
of plant polyphenols, and in particular of
tannins, which are abundant in fruits and
are qualitatively important but are often
neglected because of the diffi culties in
extracting and analysing them.

9.6 Conclusion

Polyphenols are key components of fruit
quality, responsible for important organo-
leptic properties. They are also believed to
be benefi cial to human health, but the
precise mechanisms involved need further
investigation. Fruits and berries are major
dietary sources of polyphenols, and their
composition varies qualitatively and

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