# Impact of Environmental Factors on Stilbene Biosynthesis
## 3 Impact of Environmental Factors on the Biosynthesis of Stilbenes
### Biotic Stress  
Stilbenes are well-known to act as chemical defense compounds against pathogen attack in plants [3]. Certain stilbene-producing plants constitutively biosynthetic high levels of stilbenes, independently from pathogen infection. However, in many species, the expression of stilbene biosynthetic genes and the production of stilbenes increase rapidly and conspicuously in response to pathogenic attack. For example, in the rootsof _P. cuspidatum_, large amounts of resveratrolrol and stilbene glucosides are constitutively accumulated [281; 282]. In Scots pine, high levels of pinosylvin and pinosylvin 3-O-methyl ether constitutively accumulate in the heartwood where they protect the wood against decaying fungi [283], but different stress factors including herbivore and pathogen attack can also elicit the biosynthesis of both stilbenes in sapwood and needles, where they consequently act as phytoalexins [284; 285]. In grapevine, both _STS_ gene expression and de novo synthesis of stilbenes are induced upon infection with different phytopathogenic fungi like _Botrytis cinerea_ (gray mold) [286; 287; 288], _Plasmopara viticola_ (downy mildew) [60; 290; 291], _Erysiphe necator_ (powdery mildew) [90; 292; 293], _Rhizopus stolonifer_ (black bread mold) [183], _Aspergillus_ spp. [293; 294], and _Plaeomoniella chlamdospora_ (associated with Esca and Petri diseases) [295]. To date, the impact of bacterial infection on stilbene biosynthesis in grapevine has been poorly investigated. A bacterial strain belonging to the genus _Bacillus_ has been found to elicit _trans_-resveratrol biosynthesis in _V. vinifera_ cv. Chardonnay and _V. rupestris_ in vitro-grown plantlets [296]. In 2011, [PERSON] and colleagues [297] reported that different bacterial strains originating from the vineyard such as _Pantoea agglomerans_ (Pa-AF2), _Bacillus subtilis_ (Bs-271), _Acinetobacter lwoffii_ (Al-113), and _Pseudomonas fluorescens_ (Pf-CT2) can elicit _trans_-resveratrol and _trans_-\(\varepsilon\)-viniferin biosynthesis in cells and leaves of _V. vinifera_ cv. Chardonnay. In 2015, [PERSON] and co-workers [298] investigated the ability of grapevine cv. Chardonnay plants to express immune responses at both above- and below-ground after interacting with the beneficial bacterium _P. fluorescens_ (PTA-CT2). Bacterial colonization occurred exclusively in the roots and altered the plant phenotype that exhibited multiple defense responses both locally and systemically. The interaction with bacteria-induced opposite changes in stilbene levels in leaves and roots. Significant increases in the content of _trans_-resveratrol, _trans_-piceid, and _trans_-\(\varepsilon\)-viniferin were observed in the leaves, while the content of all three stilbenes significantly decreased in the roots. This suggests that this interaction plays a role in the transfer of stilbene phytoalexins to the shoot, contributing to the systemic immune response [298]. Both [PERSON] et al. [297] and [PERSON] et al. [298] showed that defense responses triggered by the interaction with beneficial bacteria can greatly improve grapevine resistance against the fungal pathogen _B. cinerea_. Constitutive accumulation of resveratrol has been detected in several tissues of peanut plants, albeit at extremely low concentrations. A dramatic increase in both the quantity and diversity of stilbene phytoalexins can occur in response to fungal infection in peanuts [299]. In 2008, [PERSON] [300] observed that the inoculation of peanut kernels with different fungal strains belonging to the genus _Aspergillus_ strongly elicits the biosynthesis of _trans_-resveratrol, _trans_-arachidin-1, _trans_-arachidin-2, _trans_-arachidin-3, _trans_-3-isopentadienyl-4,3\({}^{\prime}\),5\({}^{\prime}\)-trihydroxystilbene, and SB-1. All tested fungal strains of _Aspergillus_ species infecting peanuts activated stilbenoid production in peanut kernel, with interesting variations among different kernel layers.