High-level tryptophan accumulation in seeds of transgenic rice and its limited effects on agronomic traits and seed metabolite profile
Kyo Wakasa1,2,*, Hisakazu Hasegawa3, Hiroshi Nemoto1, Fumio Matsuda2, Haruna Miyazawa2,4, Yuzuru Tozawa1,2, Keiko Morino2,4, Akira Komatsu1,2, Tetsuya Yamada2, Teruhiko Terakawa3
and Hisashi Miyagawa2,4
1Department of Rice Breeding, National Institute of Crop Science, 2-1-18 Kannondai, Tsukuba, Ibaraki 305-8518, Japan
2CREST, Japan Science and Technology Agency, Tokyo 103-0027, Japan
3Biochemical Laboratory, Hokko Chemical Industry Co. Ltd., 2165 Toda, Atsugi, Kanagawa 243-0023, Japan
4Division of Applied Life Science, Department of Agriculture, Kyoto University, Kyoto 606-8502, Japan
*Present address and to whom correspondence should be sent: Tokyo University of Agriculture, 1737 Funako, Atsugi, Kanagawa 243-0034, Japan. E-mail: [email protected]
Received 3 March 2006; Accepted 1 June 2006
Metabolic manipulation of plants to improve their nutritional quality is an important goal of plant biotechnology. Expression in rice (Oryza sativa L.) of a transgene (OASA1D) encoding a feedback-insensitive subunit of rice anthranilate synthase results in the accumulation of tryptophan (Trp) in calli and leaves. It is shown here that the amount of free Trp in the seeds of such plants is increased by about two orders of magnitude compared with that in the seeds of wild-type plants. The total Trp content in the seeds of the transgenic plants was also increased. Two homozygous lines, HW1 and HW5, of OASA1D transgenic rice were generated for characterization of agronomic traits and aromatic metabolite profiling of seeds. The marked overproduction of Trp was stable in these lines under field conditions, although spikelet fertility and yield, as well as seed germination ability, were reduced compared with the wild type. These differences in agronomic traits were small, however, in HW5. In spite of the high Trp content in the seeds of the HW lines, metabolic profiling revealed no substantial changes in the amounts of other phenolic compounds. The amount of indole acetic acid was increased about 2-fold in the seeds of the transgenic lines. The establishment and characterization of these OASA1D transgenic lines have thus demonstrated the feasibility of increasing the Trp content in the seeds of rice (or of other crops) as a means of improving its nutritional value for human consumption or animal feed.
Key words: Amino acids, anthranilate synthase, AS, non-containment greenhouse, IAA, isolated field, 5MT, OASA1D, Oryza sativa
Journal of Experimental Botany 2006 57(12):3069-3078. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) .