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A transgene for high methionine protein is posttranscriptionally regulated by methionine Plant
- BAGGA, SUMAN, POTENZA, CAROL, ROSS, JAMIE, MARTIN, MELINDA N., LEUSTEK, THOMAS, SENGUPTA-GOPALAN, CHAMPA
- In vitro cellular & developmental biology 2005 v.41 no.6 pp. 731-741
- Arabidopsis thaliana, alfalfa, callus, corn, metabolites, methionine, reporter genes, seed storage proteins, tobacco, transgenes
- ββ-Zein is one of the seed storage proteins of maize that is high in methionine (Met). In alfalfa, the ββ-zein gene driven by the CaMV 35S promoter showed an 8-fold lower level of transcript and protein when compared with the level in tobacco transformed with the same gene construct. The reporter gene (GUS) driven by the CaMV 35S promoter showed only a 4-fold difference between alfalfa and tobacco, suggesting that the expression of the ββ-zein gene is posttranscriptionally regulated in alfalfa. Callus of alfalfa transformants with the ββ-zein gene construct treated with exogenous Met, showed a significant increase in the ββ-zein level, suggesting that free Met may be limiting in the synthesis of ββ-zein in alfalfa. The introduction of the Arabidopsis thaliana cystathionine γγ-synthase (AtCγγS) gene driven by the CaMV 35S promoter into alfalfa showed a significant increase in the level of free Met and its metabolite, S-methyl methionine (SMM), but not in the bound fraction. Coexpression of AtCγγS and ββ-zein in alfalfa increased the level of ββ-zein transcript and protein and decreased free Met, which suggests that the ββ-zein is posttranscriptionally regulated by free Met. The expression of AtCγγS in tobacco did not produce a significant increase in free Met or SMM and coexpression of AtCγγS and ββ-zein did not result in changes in the ββ-zein level. The results demonstrate the efficacy of the synergistic approach of increasing both the sink and the source for increasing the levels of high Met ββ-zein.