Genetic and biochemical basis for alternative routes of tocotrienol biosynthesis for enhanced vitamin e antioxidant production

Chunyu Zhang, Rebecca E. Cahoon, Sarah C. Hunter, Ming Chen, Jixiang Han, Edgar B. Cahoon

Research output: Contribution to journalArticle

33 Citations (Scopus)

Abstract

Vitamin E tocotrienol synthesis in monocots requires homogentisate geranylgeranyl transferase (HGGT), which catalyzes the condensation of homogentisate and the unsaturated C20 isoprenoid geranylgeranyl diphosphate (GGDP). By contrast, vitamin E tocopherol synthesis is mediated by homogentisate phytyltransferase (HPT), which condenses homogentisate and the saturated C20 isoprenoid phytyl diphosphate (PDP). An HGGT-independent pathway for tocotrienol synthesis has also been shown to occur by de-regulation of homogentisate synthesis. In this paper, the basis for this pathway and its impact on vitamin E production when combined with HGGT are explored. An Arabidopsis line was initially developed that accumulates tocotrienols and homogentisate by co-expression of Arabidopsis hydroxyphenylpyruvate dioxygenase (HPPD) and Escherichia coli bi-functional chorismate mutase/prephenate dehydrogenase (TyrA). When crossed into the vte2-1 HPT null mutant, tocotrienol production was lost, indicating that HPT catalyzes tocotrienol synthesis in HPPD/TyrA-expressing plants by atypical use of GGDP as a substrate. Consistent with this, recombinant Arabidopsis HPT preferentially catalyzed in vitro production of the tocotrienol precursor geranylgeranyl benzoquinol only when presented with high molar ratios of GGDP:PDP. In addition, tocotrienol levels were highest in early growth stages in HPPD/TyrA lines, but decreased strongly relative to tocopherols during later growth stages when PDP is known to accumulate. Collectively, these results indicate that HPPD/TyrA-induced tocotrienol production requires HPT and occurs upon enrichment of GGDP relative to PDP in prenyl diphosphate pools. Finally, combined expression of HPPD/TyrA and HGGT in Arabidopsis leaves and seeds resulted in large additive increases in vitamin E production, indicating that homogentisate concentrations limit HGGT-catalyzed tocotrienol synthesis.

Original languageEnglish (US)
Pages (from-to)628-639
Number of pages12
JournalPlant Journal
Volume73
Issue number4
DOIs
StatePublished - Feb 1 2013

Fingerprint

Tocotrienols
tocotrienols
Vitamins
Molecular Biology
vitamins
Antioxidants
biosynthesis
antioxidants
Dioxygenases
Transferases
transferases
Vitamin E
synthesis
vitamin E
Arabidopsis
Tocopherols
isoprenoids
Terpenes
tocopherols
Prephenate Dehydrogenase

Keywords

  • homogentisate
  • homogentisate geranylgeranyl transferase
  • homogentisate phytyltransferase
  • tocopherol
  • tocotrienol
  • vitamin E

ASJC Scopus subject areas

  • Genetics
  • Plant Science
  • Cell Biology

Cite this

Genetic and biochemical basis for alternative routes of tocotrienol biosynthesis for enhanced vitamin e antioxidant production. / Zhang, Chunyu; Cahoon, Rebecca E.; Hunter, Sarah C.; Chen, Ming; Han, Jixiang; Cahoon, Edgar B.

In: Plant Journal, Vol. 73, No. 4, 01.02.2013, p. 628-639.

Research output: Contribution to journalArticle

Zhang, Chunyu ; Cahoon, Rebecca E. ; Hunter, Sarah C. ; Chen, Ming ; Han, Jixiang ; Cahoon, Edgar B. / Genetic and biochemical basis for alternative routes of tocotrienol biosynthesis for enhanced vitamin e antioxidant production. In: Plant Journal. 2013 ; Vol. 73, No. 4. pp. 628-639.
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AU - Chen, Ming

AU - Han, Jixiang

AU - Cahoon, Edgar B.

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N2 - Vitamin E tocotrienol synthesis in monocots requires homogentisate geranylgeranyl transferase (HGGT), which catalyzes the condensation of homogentisate and the unsaturated C20 isoprenoid geranylgeranyl diphosphate (GGDP). By contrast, vitamin E tocopherol synthesis is mediated by homogentisate phytyltransferase (HPT), which condenses homogentisate and the saturated C20 isoprenoid phytyl diphosphate (PDP). An HGGT-independent pathway for tocotrienol synthesis has also been shown to occur by de-regulation of homogentisate synthesis. In this paper, the basis for this pathway and its impact on vitamin E production when combined with HGGT are explored. An Arabidopsis line was initially developed that accumulates tocotrienols and homogentisate by co-expression of Arabidopsis hydroxyphenylpyruvate dioxygenase (HPPD) and Escherichia coli bi-functional chorismate mutase/prephenate dehydrogenase (TyrA). When crossed into the vte2-1 HPT null mutant, tocotrienol production was lost, indicating that HPT catalyzes tocotrienol synthesis in HPPD/TyrA-expressing plants by atypical use of GGDP as a substrate. Consistent with this, recombinant Arabidopsis HPT preferentially catalyzed in vitro production of the tocotrienol precursor geranylgeranyl benzoquinol only when presented with high molar ratios of GGDP:PDP. In addition, tocotrienol levels were highest in early growth stages in HPPD/TyrA lines, but decreased strongly relative to tocopherols during later growth stages when PDP is known to accumulate. Collectively, these results indicate that HPPD/TyrA-induced tocotrienol production requires HPT and occurs upon enrichment of GGDP relative to PDP in prenyl diphosphate pools. Finally, combined expression of HPPD/TyrA and HGGT in Arabidopsis leaves and seeds resulted in large additive increases in vitamin E production, indicating that homogentisate concentrations limit HGGT-catalyzed tocotrienol synthesis.

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