# Impact of Environmental Factors on Stilbene Biosynthesis
## 3 Impact of Environmental Factors on the Biosynthesis of Stilbenes
### UV Radiation  
Multiple lines of evidence indicate that stilbenes, as well as other polyphenols, play an important role in protecting plants from the damaging effects of ultraviolet (UV) radiation [243; 244; 245]. Induction of polyphenolic phytoplankton biosynthesis in response to UV exposure has been observed in numerous plants [246; 247]. Non-polyphenylonic phytoalexins can also be elicited by UV, e.g., labdane-related diterpenoids in rice [248] and terpenoid indole alkaloids in the Madagascar periiwinkle (_Catharanthus roseus_ (L) G.Don) [249]. The solar UV spectrum is conventionally subdivided into three wavelength ranges: UV-A (315-400 nm), UV-B (280-315 nm), and UV-C (100-280 nm) [250]. UV-C is extremely harmful to organisms, but it is naturally filtered by the stratospheric ozone layer and it is consequently not relevant under natural conditions of solar irradiation. Ozone absorption coefficient drops rapidly at wavelengths longer than 280 nm, reaching zero around 330 nm, therefore UV-B and UV-A can reach Earth's surface and interact with plants [251]. However, UV harmfulness declines in a similar way, as UV-A cannot be absorbed by DNA and it is thus far less damaging for plants [252]. As a result, for a long time, the effects of UV-A on plant physiology had been underestimated and most studies have focused primarily on UV-C and subordinately on UV-B. UV-C significantly increases stilbene production in different stilbene-producing plants including grapevine [92; 184; 253; 194], peanut [254; 255; 216], _Gnetum parvifolium_ ([PERSON].) [PERSON]. [PERSON] [204; 205], _Picea jezconsis_ ([PERSON] & Zucc.) [PERSON]. [255], and _Polygonum cuspidatum_ [PERSON] and [PERSON]. [256] (Table 1). Recently, [PERSON] and colleagues [60] performed a genome-wide analysis of the _VvSTS_ multigene family expression pattern on _V. vinifera_ cv. Pinot Nair ('PN40024' genotype) leaf disks subjected to different stresses (i.e., UV-C exposure, wounding, and downy mildew infection) through a whole transcriptomic (RNA-seq) and real-time qRT-PCR approach. They observed that all stress treatments led to a significant up-regulation of at least several members of the _VvSTS_ multigene family. However, UV-C exposure resulted in the highest induction of the majority of _VvSTS_ members. The induction of _VvSTS_s was accompanied by reduced expression of _VvCHS_ genes to lower levels compared to untreated leaf discs, suggesting that the competitive relationship between _VvSTS_ and _VvCHS_ may play a role in the accumulation of stilbenes in response to UV-C [60; 198]. Molecular mechanisms behind the induction of stilbene biosynthesis in response to UV radiation are still not completely understood. The induction is accompanied by transcriptional activation, protein accumulation, and activation of STS and other enzymes involved in stilbene biosynthesis [5]. In 2013, [PERSON] and co-workers [257] reported that two R2R3-MYB-type transcription factors, namely _MYB14_ and _MYB15_, control the transcriptional expression of _VvSTS_ genes under UV-C irradiation in _V. vinifera_ cv. Shiraz leaf discs. However, these transcription factors appear not to be specifically involved in response to UV-C, but also to other stresses including fungal infections and wounds. In a recent study, the member of the stilbene synthase family _VvSTS29_ derived from Chinese wild _Vitis pseudoreticulata_ W.T. [PERSON] was overexpressed in _V. vinifera_ cv. Thompson Seedless and the localization of the VpSTS29-GFP protein was investigated [247]. The accumulation of stilbenes elicited by UV-C irradiation was accompanied by the translocation of the VpSTS29-GFP protein from the cytoplasm to the chloroplast. Interestingly, transgenic plants overexpressing VpSTS29-GFP exhibited much lower H\({}_{2}\)O\({}_{2}\) content than untransformed plants and an altered expression of genes related to redox processes, stilbene biosynthesis, and light stimulus [247].