EXPRESSION OF THE BRAZIL NUT METHIONINE-RICH PROTEIN AND MUTANTS WITHINCREASED METHIONINE IN TRANSGENIC POTATO

A cDNA encoding the methionine-rich(19 mol% Met) protein in Brazil nut was placed under the regulation of CaMV 35S promoter and nopaline syn thase terminator and introduced into the potato cultivar Russet Burban k via Agrobacterium-mediated transformation. To further enhance the Me t content in the transgenic plants, chimeric genes containing four mut ant constructs, BoxIa (with 5 additional Met), BoxIIa (2 additional Me t), BoxIaIIa (7 additional Met), and BoxIIa(2) (7 additional Met), wer e also generated by sequence modifications of the cDNA and transferred into potato. Analysis of the microtubers and leaves of the transgenic potato plants revealed, in general, with the exception of the BoxIIa( 2), the presence of mRNA transcripts of the expected size and the corr ectly processed Met-rich 9 kDa subunit polypeptides. The expression le vels in the leaves among the various constructs and individual transge nic plants varied between <0.01% and 0.2% of total protein. The corres ponding expression in the tubers was usually 2- to 4-fold lower than i n leaves. In the case of BoxIIa(2), which contains two tandem repeats of the BoxIIa mutant sequence, a larger (10.5-11 kDa) polypeptide was detected. These findings demonstrated that it is feasible to exploit t he variable region of the Brazil Nut 2S protein for enhanced Met conte nts and perhaps for other desirable properties.