High-level tryptophan accumulation in seeds of transgenic rice and its limited effects on agronomic traits and seed metabolite profile

Abstract

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 alpha 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.

Advances in detection of stress tolerance in plants through metabolomics approaches

“…Metabolomics studies in rice have so far demonstrated that the various metabolites can improve seed germination (Moongngarm and Saetung, 2010). The uniqueness of metabolites amongst wild type and mutant plants (Wakasa et al, 2006), the metabolome profiling at several phases of improvement (Tarpley et al, 2005), and the analysis of normal metabolite distinction amid altered rice varieties has been reported (Kusano et al, 2011).…”

The contribution of transgenic plants to better health through improved nutrition: opportunities and constraints

“…The key rate-limiting enzyme in tryptophan synthesis is anthranilate synthase, which catalyzes the conversion of chorismate to anthranilate, and tryptophan levels in rice have been increased more than 400-fold by expressing a feedback-insensitive version (Wakasa et al 2006). Tryptophan levels also increased 30-fold in potato tubers (Yamada et al 2004) and 20-fold in soybean seeds (Ishimoto et al 2010) expressing feedback-insensitive AS.…”

Challenges for Metabolomics as a Tool in Safety Assessments

“…Although there are complexities in the interpretation of data generated through modern profiling technologies (Broadhurst and Kell, 2006;Lay et al, 2006) including the fact that the data is not quantitative and there is no standardized framework for comparisons, the lack of variation between GM crops and their conventional comparators at the transcriptomic, proteomic, and metabolomic level has, nonetheless, been independently corroborated. These profiling evaluations extend to a wide range of plants including wheat (Baker et al, 2006;Gregersen et al, 2005;Ioset et al, 2007), potato (Catchpole et al, 2005;Defernez et al, 2004;Lehesranta et al, 2005), soybean (Cheng et al, 2008), rice (Dubouzet et al, 2007;Wakasa et al, 2006), tomato (Le Gall et al, 2003), tobacco, Arabidopsis (Kristensen et al, 2005), and Gerbera (Ainasoja et al, 2008).…”