title: RNAi suppression of Arogenate Dehydratase1 reveals that phenylalanine is synthesized predominantly via the arogenate pathway in petunia petals.
abstract: l-Phe, a protein building block and precursor of numerous phenolic compounds, is synthesized from prephenate via an arogenate and/or phenylpyruvate route in which arogenate dehydratase (ADT) or prephenate dehydratase, respectively, plays a key role. Here, we used Petunia hybrida flowers, which are rich in Phe-derived volatiles, to determine the biosynthetic routes involved in Phe formation in planta. Of the three identified petunia ADTs, expression of ADT1 was the highest in petunia petals and positively correlated with endogenous Phe levels throughout flower development. ADT1 showed strict substrate specificity toward arogenate, although with the lowest catalytic efficiency among the three ADTs. ADT1 suppression via RNA interference in petunia petals significantly reduced ADT activity, levels of Phe, and downstream phenylpropanoid/benzenoid volatiles. Unexpectedly, arogenate levels were unaltered, while shikimate and Trp levels were decreased in transgenic petals. Stable isotope labeling experiments showed that ADT1 suppression led to downregulation of carbon flux toward shikimic acid. However, an exogenous supply of shikimate bypassed this negative regulation and resulted in elevated arogenate accumulation. Feeding with shikimate also led to prephenate and phenylpyruvate accumulation and a partial recovery of the reduced Phe level in transgenic petals, suggesting that the phenylpyruvate route can also operate in planta. These results provide genetic evidence that Phe is synthesized predominantly via arogenate in petunia petals and uncover a novel posttranscriptional regulation of the shikimate pathway.
authors.affiliation: Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Maeda
authors.forename: Ajit K
authors.initials: AK
authors.lastname: Shasany
authors.forename: Jennifer
authors.initials: J
authors.lastname: Schnepp
authors.forename: Irina
authors.initials: I
authors.lastname: Orlova
authors.forename: Goro
authors.initials: G
authors.lastname: Taguchi
authors.forename: Bruce R
authors.initials: BR
authors.lastname: Cooper
authors.forename: David
authors.initials: D
authors.lastname: Rhodes
authors.forename: Eran
authors.initials: E
authors.lastname: Pichersky
authors.forename: Natalia
authors.initials: N
authors.lastname: Dudareva
mesh_terms: D000600:Amino Acids, Dicarboxylic / Q000378:metabolism; D053138:Cyclohexenes / Q000378:metabolism; D035264:Flowers / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D006836:Hydro-Lyases / Q000235:genetics / Q000378:metabolism*; D032306:Petunia / Q000201:enzymology / Q000235:genetics*; D010649:Phenylalanine / Q000096:biosynthesis*; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics; D034622:RNA Interference; D018749:RNA, Plant / Q000235:genetics; D012765:Shikimic Acid / Q000378:metabolism; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism; D055549:Volatile Organic Compounds / Q000032:analysis
chemical_list: D000600:Amino Acids, Dicarboxylic; D053138:Cyclohexenes; D010940:Plant Proteins; D018749:RNA, Plant; D055549:Volatile Organic Compounds; D012765:Shikimic Acid; D014443:Tyrosine; D010649:Phenylalanine; C015478:pretyrosine; D006836:Hydro-Lyases; C022437:pretyrosine dehydratase