InterPro2GO mapping of the chalcone/stilbene synthase and type III polyketide synthase domain signatures supplied the broad acyltransferase-activity molecular-function annotations reviewed in this file.

SwissProt keyword-derived (SPKW) annotations present in the Sept 2025 goa_uniprot_gcrp snapshot but removed from the current GOA release after GOA retired the keyword2GO pipeline for cellular organisms.

Mapping of the UniProt subcellular location "Cytoplasm" supplied the cytoplasm cellular-component annotation reviewed in this file.

Combined multi-method IEA annotation supplied the precise trihydroxystilbene synthase activity (GO:0050350, EC 2.3.1.95) molecular-function annotation reviewed in this file.

STS3 (VvSTS3) is a type III polyketide synthase (stilbene/resveratrol synthase, EC 2.3.1.95) that catalyzes the committed step of the stilbenoid branch of the phenylpropanoid pathway, condensing one p-coumaroyl-CoA starter with three malonyl-CoA extenders to form trans-resveratrol.

trans-Resveratrol and derived stilbenoids are treated as phytoalexins - defense-associated metabolites whose synthesis is strongly induced by biotic and abiotic stress (e.g., UV-C induced resveratrol accumulation ~196x over control at 16 h, with parallel biphasic induction of STS mRNA and protein); the defense role is a property of the metabolite product, while the enzyme itself performs a biosynthetic synthase function.

STS belongs to a large diversified grapevine multigene family; reviews emphasize that clear experimental evidence for distinct substrate specificities among individual grape STS paralogs remains limited, and no 2024 primary paper directly re-characterizes VvSTS3/P51071 biochemistry.

Immunolocalization in young grape plants placed STS protein predominantly in the cytoplasm and cell wall, with additional signal in chloroplasts and vacuoles and tissue enrichment in phloem, consistent with a soluble cytosolic enzyme.

STS family expression is coordinated by subgroup 2 R2R3-MYB (MYB14/MYB15) and WRKY transcription factors that reprogram carbon flux toward stilbenoid biosynthesis; VvSTS3 has been used as an engineered resveratrol-production module in heterologous plant cell systems.

STS3 catalyzes 4-coumaroyl-CoA + 3 malonyl-CoA + 3 H+ = trans-resveratrol + 4 CO2 + 4 CoA (EC 2.3.1.95, Rhea:RHEA:11936); it is a cytoplasmic homodimer of the chalcone/stilbene synthase (thiolase-like) family, induced by stress.

Stilbene synthase and PAL are key enzymes of the biosynthetic pathway to stilbene phytoalexins; their mRNAs are co-induced within 1 h of fungal cell-wall elicitor treatment of grape cell cultures.

The grapevine genome contains an unusually large STS gene family (48 STS genes, >=32 potentially functional); STS evolved from CHS several times independently, and characterized grapevine STS genes encode bona fide STS activity.

STS and CHS use the same phenylpropanoid starter and three malonyl-CoA to form a common tetraketide intermediate, then use different cyclization mechanisms; an "aldol switch" in STS directs aldol cyclization to form the stilbene scaffold.

CHS condenses one p-coumaroyl-CoA and three malonyl-CoA into a polyketide intermediate that cyclizes; the CHS-resveratrol complex shows how the related stilbene synthase uses the same substrates and an alternate cyclization pathway.

STS is the key enzyme of stilbenic phytoalexin biosynthesis; individual grapevine STS genes are transcriptionally induced by powdery mildew infection and regulated developmentally.

Resveratrol (1 mM) inhibits mycelial growth of Phytophthora palmivora in vitro; heterologous expression of a grapevine STS gene increases pathogen resistance in papaya.

Grapevine STS expressed in white poplar produces resveratrol glucosides, but accumulation of the phytoalexin did not increase rust resistance, showing the STS enzyme is one biosynthetic input rather than a complete defense program.

STS expression and stilbenoid levels increase in response to powdery mildew infection; overexpression of an STS gene raises stilbenoid accumulation and disease resistance in grapevine.