Enhancement of the methionine content of seed proteins by the expression of a chimeric gene encoding a methionine-rich protein in transgenic plants

Abstract

We have constructed a chimeric gene encoding a Brazil nut methionine-rich seed protein which contains 18% methionine. This gene has been transferred to tobacco and expressed in the developing seeds. Tobacco seeds are able to process the methionine-rich protein efficiently from a larger precursor polypeptide of 17 kDa to the 9 kDa and 3 kDa subunits of the mature protein, a procedure which involves three proteolytic cleavage steps in the Brazil nut seed. The accumulation of the methionine-rich protein in the seeds of tobacco results in a significant increase (30%) in the levels of the methionine in the seed proteins of the transgenic plants. Our data indicate that the introduction of a chimeric gene encoding a methionine-rich seed protein into crop plants, particularly legumes whose seeds are deficient in the essential sulfur-containing amino acids, represents a feasible method for improving the nutritional quality of seed proteins.

Next-generation protein-rich potato expressing the seed protein gene AmA1 is a result of proteome rebalancing in transgenic tuber

“…However, there is currently public concern about the use of genetically engineered foods in contemporary agriculture, particularly when genes are from a nonplant source. During the past decade, several potential candidate genes have been targeted for the nutritional improvement of protein content in crops, namely: Brazil nut 2S albumin (13), AmA1 (Amaranth Albumin 1) (14), β-phaseoline (15), HS-7 zein (3), cruciferin (16), sunflower seed albumin (17), and S-rich zein (18). However, excepting AmA1 (14,19,20), introduction of these genes in target plants has often resulted in an increase in one of the amino acids at the expense of others, leading to an imbalance of the amino acid profile in transgenic crops.…”

Increased nutritive value of transgenic potato by expressing a nonallergenic seed albumin gene from Amaranthus hypochondriacus

“…Although the 2S albumins from Brazil nut and sunflower contain 18% methionine͞8% cysteine and 16% methionine͞8% cysteine, respectively, they have lower levels of other essential amino acids. Eventually, when introduced in target plants, they resulted in dramatic increase only in methionine, along with a significant decrease in cysteine content (25,26). This result reduces the usefulness of such proteins as a means of improving nutritional quality of recipient plants if they are deficient in any other essential amino acids.…”

Genetic contributions to agricultural sustainability

“…Importantly, the methionine was also of benefit to sheep due to the rumen stability of the added methionine-rich sink protein (White et al 2001). The Brazil nut 2S albumin has been expressed in a number of seeds including tobacco, canola, narbon bean and soya bean, with increases in total seed methionine of 30-100% when compared with wildtype (Altenbach et al 1989(Altenbach et al , 1992Muntz et al 1997;Tabe & Higgins 1998). The levels of seed methionine in the GM soya beans and narbon beans were predicted to be sufficient for optimal animal nutrition; however, the potential human allergenicity of the Brazil nut protein has prevented it from being used commercially.…”