# Impact of Environmental Factors on Stilbene Biosynthesis
## 2 Biosynthesis of Stilbenes and Stilbenoids
### Stilbene Synthas
CHS and STS are the most investigated enzymes among PKSs and, due to their high sequence similarity, they are often referred to as the CHS/STS family [63; 64]. Although it employs the same substrates as STS, CHS is responsible for the first committed step in the biosynthesis of flavonoid-type compounds. Both enzymes generate the same linear tetraketide intermediate. However, CHS catalyzes a C6\(\rightarrow\)C1 Claisen condensation of the intermediate to produce naringenin chalcone, while STS catalyzes an alternative C2\(\rightarrow\)C7 aldol condensation of the intermediate to form a stilbene backbone (Figure 4) [59; 65; 66]. STS was first extracted and purified from suspension cultures of peanut cells elicited with UV radiation [53]. Cloning of two peanut _STS_ genes revealed a high sequence identity with _CHS_ throughout the coding region and the presence of an intron at the same position as a conserved intron in _CHS_[67]. _STS_ genes and cDNAs were subsequently cloned and characterized from grapevine cell suspension cultures [68] and Scots pine plantlets [56], both induced by fungal elicitors. At present, _STS_ genes have been cloned from several plant species including mulberry (_Morus notabilis_ [PERSON]. [PERSON] and _M. atropurpurea_ [PERSON].) [66; 42], Scots pine [69], white spruce (_Picea glauca_ ([PERSON]) [70], Norway spruce (_Picea abies_ ([PERSON]) [71], Japanese red pine [57], and sorghum (_Sorghum bicolor_ ([PERSON]) [72]. To the best of our knowledge, sorghum is the only monocot plant in which an _STS_ gene (_SbSTS1_) has been identified. In most stilbene-producing plants, _STS_ exists as a small family consisting of 1-10 closely related paralogs. For example, the _STS_ multigene family is represented by two members in white spruce [70] and Norway spruce [71], three members in Japanese red pine [57], almost five members in Scots pine [69], six members in peanut [73], and ten members in mulberry [66]. Remarkable exceptions to this role are sorghum, in whose genome only one _STS_ gene has been identified [74; 75], and grapevine, which possesses an uncommonly large number of _STS_ genes. Both grapevine and sorghum genomes have been entirely sequenced [74; 76]. Early Southern-blot analysis suggested that the grapevine _STS_ gene family consisted of 15-20 members [77]. Genome-wide analysis carried out on the _V. vinifera_ PN40024 genome led to the identification of 48 putative _STS_ genes, designated _VvSTS1_ to _VvSTS48_, with at least 33 potentially coding for functional STS proteins [60; 62]. To date, there is no evidence regarding the different substrate specificity and enzymatic activity of different _VvSTS_s. Functional characterization of nine _VvSTS_s confirmed that they encode for functional STS enzymes [62]. Since these nine genes were specifically chosen to represent the diversity of the _VvSTS_ gene family, it is most likely that all grapevine _VvSTS_s encode enzymes with similar activity and specificity. Despite the high similarity between _STS_ genes which makes it difficult to accurately distinguish the individual transcripts, gene expression studies revealed different transcriptional responses of distinct _VvSTS_s during development and in response to environmental stresses [60; 78; 79]. The expression of some _VvSTS_s was also found to be tissue-specific [60; 79]. It is therefore likely that the large quantity of members in the grapevine _STS_ gene family has evolved to allow for fine spatial and temporal regulation of stilbene biosynthesis under both normal and stress conditions.