Article

Plant Molecular Biology

, Volume 75, Issue 6, pp 555-565

First online:

Open Access This content is freely available online to anyone, anywhere at any time.

Mechanism of gallic acid biosynthesis in bacteria (Escherichia coli) and walnut (Juglans regia)

  • Ryann M. MuirAffiliated withDepartment of Plant Sciences, University of California
  • , Ana M. IbáñezAffiliated withDepartment of Plant Sciences, University of California
  • , Sandra L. UratsuAffiliated withDepartment of Plant Sciences, University of California
  • , Elizabeth S. InghamAffiliated withDepartment of Plant Sciences, University of California
  • , Charles A. LeslieAffiliated withDepartment of Plant Sciences, University of California
  • , Gale H. McGranahanAffiliated withDepartment of Plant Sciences, University of California
  • , Neelu BatraAffiliated withDepartment of Plant Sciences, University of California
  • , Sham GoyalAffiliated withDepartment of Plant Sciences, University of California
  • , Jorly JosephAffiliated withDepartment of Inorganic and Physical Chemistry, Indian Institute of Science
    • , Eluvathingal D. JemmisAffiliated withDepartment of Inorganic and Physical Chemistry, Indian Institute of Science
    • , Abhaya M. DandekarAffiliated withDepartment of Plant Sciences, University of California Email author 

Abstract

Gallic acid (GA), a key intermediate in the synthesis of plant hydrolysable tannins, is also a primary anti-inflammatory, cardio-protective agent found in wine, tea, and cocoa. In this publication, we reveal the identity of a gene and encoded protein essential for GA synthesis. Although it has long been recognized that plants, bacteria, and fungi synthesize and accumulate GA, the pathway leading to its synthesis was largely unknown. Here we provide evidence that shikimate dehydrogenase (SDH), a shikimate pathway enzyme essential for aromatic amino acid synthesis, is also required for GA production. Escherichia coli (E. coli) aroE mutants lacking a functional SDH can be complemented with the plant enzyme such that they grew on media lacking aromatic amino acids and produced GA in vitro. Transgenic Nicotiana tabacum lines expressing a Juglans regia SDH exhibited a 500% increase in GA accumulation. The J. regia and E. coli SDH was purified via overexpression in E. coli and used to measure substrate and cofactor kinetics, following reduction of NADP+ to NADPH. Reversed-phase liquid chromatography coupled to electrospray mass spectrometry (RP-LC/ESI–MS) was used to quantify and validate GA production through dehydrogenation of 3-dehydroshikimate (3-DHS) by purified E. coli and J. regia SDH when shikimic acid (SA) or 3-DHS were used as substrates and NADP+ as cofactor. Finally, we show that purified E. coli and J. regia SDH produced GA in vitro.

Keywords

AroE Gallic acid Juglans regia Escherichia coli Shikimate dehydrogenase Walnut Tannins