The molecular regulation of stilbene
phytoalexin biosynthesis in developing Vitis vinifera L.
grape berries was investigated using a UV induction system. Berries were
collected at 1, 5, 10 and 16 weeks post-flowering from the cultivars Shiraz,
Semillon, Cabernet Sauvignon and Chardonnay and the skins analysed for
resveratrol production following irradiation with UV-C light. The rate and
maximal level of resveratrol accumulation increased markedly in berries
sampled from 1–5 weeks post-flowering and then dramatically declined in
maturing berries sampled from 10–16 weeks post-flowering in all
cultivars. In berries sampled at 1 and 5 weeks post-flowering, maximal levels
of resveratrol accumulation were recorded at incubation periods of 24 and 48 h
respectively whereas maximal resveratrol levels were not recorded in week 16
berry skins until 72 h after UV-treatment. Gene expression analysis indicated
that stilbene synthase (STS) mRNA accumulated within 4–8 h of UV
treatment in berries sampled at 1 and 5 weeks post-flowering, but did not
increase in week 16 berries until 24–48 h following UV-irradiation.
Furthermore, the overall level of STS gene expression declined in berries
sampled 10–16 weeks post-flowering. The results demonstrate that
inducible stilbene accumulation in ripening grape berries is highly regulated
at the level of STS gene transcription. This decline in inducible STS gene
expression may be a major factor contributing to the increased susceptibility
of ripening grape berries to Botrytis cinerea infection.
Coexpression of Sucrose Synthase and the SWEET Transporter, Which Are Associated With Sugar Hydrolysis and Transport, Respectively, Increases the Hexose Content in Vitis vinifera L. Grape Berries
