Poster: Metabolic Engineering

Abs # 1015: Metabolic engineering of tocopherol biosynthesis for increased tocopherol content in Arabidopsis and Synechocystis sp. PCC6803

Presenter:	Qi, Qungang , qungang.qi@monsanto.com
Authors	Qi, Qungang  (A)   Karunanandaa, Balasulojini  (A)   Hao, Ming  (A)   Baszis, Susan  (A)   Wong, Yun-hua  (A)   Jiang, Jian  (A)   Jensen, Pamela  (A)   Warren, Aundrea  (A)   Moshiri, Fred  (A)   Gruys, Kenneth J.  (A)   Venkatramesh, Mylavarapu  (A)   Valentin, Henry E  (A)
Affiliations:	(A): Monsanto Company

Tocopherols are important natural lipid-soluble substances that belong to the group of vitamin E compounds. The compounds are synthesized by plants and certain photosynthetic bacteria, and well recognized as effective antioxidant scavengers in foods and biological systems. An elevation of a-tocopherol content in Arabidopsis seeds has been recently demonstrated through manipulation of g-tocopherol methyltransferase (Shintani and DellaPenna, Science, 1998, 282: 2098-2100). In present study, the photosynthetic model organism Synechocystis and Arabidopsis were genetically engineered through over-expression of genes involved in tocopherol precursor synthesis for enhanced accumulation of tocopherols. A bifunctional prephenate dehydrogenase (tyrA), p-hydroxyphenylpyruvate dioxygenase (HPPD), geranylgeranylpyrophosphate reductase (GGH), and a homogentisate prenyltransferase (HPT) were expressed as a single gene or gene combinations under the Lac promoter in Synechocystis or seed-specific promoter in Arabidopsis. Over-expression of these genes led to an elevated synthesis of the tocopherol precursors homogentisate and phytyldiphosphate as well as the increased corresponding enzyme activity and protein levels. Coordinated expression of tyrA, HPPD, GGH, HPT in Synechocystis resulted in a total tocopherol increase of 16.5-fold, relative to the wild-type. Similarly, when HPPD, tyrA, and HPT were expressed in Arabidopsis seeds, tocopherol levels increased up to 5-fold. To our knowledge, this is the first report that shows a dramatic increase in total tocopherol content of transgenic Synechocystis and plants. This work and previous studies now provide the tools for precise tailoring of oil seed tocopherol content and composition to optimize for oil stability and nutritional value.