title: Transgenic rice grains expressing a heterologous ρ-hydroxyphenylpyruvate dioxygenase shift tocopherol synthesis from the γ to the α isoform without increasing absolute tocopherol levels.
abstract: We generated transgenic rice plants overexpressing Arabidopsis thaliana ρ-hydroxyphenylpyruvate dioxygenase (HPPD), which catalyzes the first committed step in vitamin E biosynthesis. Transgenic grains accumulated marginally higher levels of total tocochromanols than controls, reflecting a small increase in absolute tocotrienol synthesis (but no change in the relative abundance of the α and γ isoforms). In contrast, there was no change in the absolute tocopherol level, but a significant shift from the γ to the α isoform. These data confirm HPPD is not rate limiting, and that increasing flux through the early pathway reveals downstream bottlenecks that act as metabolic tipping points.
authors.affiliation: Departament de Producció Vegetal i Ciència Forestal, Universitat de Lleida-CRA, 25198, Lleida, Spain.
authors.forename: Gemma
authors.initials: G
authors.lastname: Farré
authors.forename: Duraialagaraja
authors.initials: D
authors.lastname: Sudhakar
authors.forename: Shaista
authors.initials: S
authors.lastname: Naqvi
authors.forename: Gerhard
authors.initials: G
authors.lastname: Sandmann
authors.forename: Paul
authors.initials: P
authors.lastname: Christou
authors.forename: Teresa
authors.initials: T
authors.lastname: Capell
authors.forename: Changfu
authors.initials: C
authors.lastname: Zhu
mesh_terms: D015111:4-Hydroxyphenylpyruvate Dioxygenase / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D015152:Blotting, Northern; D003001:Cloning, Molecular; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D012275:Oryza / Q000201:enzymology* / Q000235:genetics; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D012639:Seeds / Q000201:enzymology* / Q000235:genetics; D014170:Transformation, Genetic; D024502:alpha-Tocopherol / Q000378:metabolism*; D024504:gamma-Tocopherol / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D018749:RNA, Plant; D024504:gamma-Tocopherol; D015111:4-Hydroxyphenylpyruvate Dioxygenase; D024502:alpha-Tocopherol