Enhancement of Vitamin E Level in Oilseeds through Metabolic Engineering.

点击翻译按钮获取中文摘要

(1)Three cDNAs encoding respective enzymes in the tocopherol biosynthetic pathway, namely HPT (homogentisate phytyltransferase), MPBQMT (MPBQ methyltransferase) and TC (tocopherol cyclase), were cloned and characterized from sesame, S.indicum. We, thus, have obtained each of the cDNA clones cording for enzymes which catalyze the successive reaction steps from homogentisic acid to vitamin E (α-tocopherol) in sesame because of our previous isolation of sesameγ-TMT (γ-tocopherol methyltransferase) cDNA. A genomic DNA clone for γ-TMT was also isolated from sesame and its nucleotide sequence was determined.(2)Several genes for fatty-acid desaturases or storage proteins are known to express strongly and specifically during seed development in sesame. We tried to isolate genomic DNAs containg 5'-upstream regulatory regions of such genes, and succeeded for desaturase genes of Δ9 and a microsomal ω-6, and genes of oleosin and 2S albumin. These 5'-upstream regions were sequenced, and the first nucleotides in their transcripts were detected by the Capsite mapping mehtod.(3)The sesame γ-TMT cDNA was ligated to each of the 5'-upstream regions of Δ9 desaturase, oleosin and 2S albumin genes isolated from sesame, or to that of G1 glycinin gene derived from soybean. Such chimera genes were respectively introduced to seedlings of a wild sesame, S.schrxizianum by infection of Agrobacterium with the MAT vector system. For soybean G1 glycinin :: γ-TMT, all the transgenic plants produced immature seeds which seldom germinated. For sesame oleosin :: γ-TMT and sesame 2S albumin :: γ-TMT, the transgenic plants are now during vegetative growth, and for sesameΔ9 desaturase :: γ-TMT, efficient formation of crown galls are observed on the seedlings at present.