conference schedule and program with abstracts - Horticulture ...

O-21
Identification and functional characterization of potential targets for genetic improvement
of grape berry quality
I. Hichri, C. Kappel, A. Mahjoub, P. Nicolas, J. Pillet, C. Vignault, F. Barrieu, A. Destrac, S.
Guillaumie, G. Hilbert, F. Lecourieux, D. Lecourieux, V. Lauvergeat, C. Léon, P. Pieri, C.
Trossat, E. Gomes, S. Delrot*
Centre INRA Bordeaux-Aquitaine, France
*Corresponding author: serge.delrot@bordeaux.inra.fr
Grape berry and wine quality and typicity depend on fruit metabolite content (sugars, organic
acids, flavonoids, aroma precursors). This content results from complex interactions between two
genotypes (rootstock and variety) and the environment. Genetic selection requires identification
of genome regions and genes which control the metabolism and accumulation of these
compounds. Our lab has developed several strategies that may lead to this identification. Based
on previous data with model plants, targeted approaches using PCR and a wide range of
functional genomic tools (transcriptomics, transient and stable transformation) led us to identify
several transcription factors (belonging to Myb and Wky families) and regulatory proteins
(protein kinases) involved in either the control of sugar transport or secondary metabolism.
VvSK1, a GSK3 protein kinase, is strongly expressed at post-véraison, when the berries
accumulate glucose, fructose, and abscisic acid (ABA). In grapevine cell suspensions, VvSK1
transcript abundance is increased by sugars and ABA. VvSK1 overexpression in grapevine cells
increased the transcript abundance of four monosaccharide transporters. At the same time, the
rate of glucose uptake was increased three to five fold and the amount of glucose and sucrose in
the cells was doubled, while the starch amount was not affected. Overexpression of VvWKY2 in
tobacco induces drastic modifications in lignin composition, especially the Syringyl/Guaiacyl
ratio, in xylem vessel diameter, and alters the organization of the vascular structure. Transient
expression in tobacco protoplasts showed that VvWRKY2 activates the promoter of the
grapevine C4H. Overexpression of VvMYB5b in tomato induced pleiotropic changes including
dwarfism, modified leaf structure, alterations of floral morphology, pigmented and glossy fruits
at the “green-mature” stage, and impaired seed germination. VvMYB5b overexpression
downregulated the phenylpropanoid pathway whereas carotenoid metabolism was upregulated.
The strongest modification was a decrease in beta-amyrin, the precursor of the oleanolic acid,
which is the major component of grape waxes. VvMYC1, a member of the bHlH family, was
characterized as a component of the transcriptional complexes controlling anthocyanin and
proanthocyanidin biosynthesis during the development of grape berries. Non-targeted approaches
are now developed to identify regulatory genes controlling the response of berry metabolism to
changes in the microenvironment (light, temperature). These approaches and results will be
illustrated.
41