Genetic engineering ruminal stable high methionine protein in the foliage of alfalfa

Alfalfa and other forage legumes are high in protein but deficient in S-amino acids cysteine and methionine. Our long-term goal is to improve the protein content of forage legumes for ruminants by introducing into them functional genes encoding for proteins rich in sulfur amino acids that are ruminally stable. The delta- and beta-zein proteins contain proportionately high levels of S-amino acids and the focus of this paper is to determine if the introduction of the zein genes into alfalfa is a valid approach towards improving the methionine content of alfalfa leaves. Towards accomplishing our goal we have transformed alfalfa with CaMV 35S-beta-zero and CaMV 35S-delta-zein gene constructs individually and in combination. Our results demonstrate that as in tobacco both the beta- and the delta-zeins accumulate in the leaves of alfalfa and that the co-expression of the two zein genes has a stabilizing effect on the delta-zero. However, the level of accumulation of the zeins in alfalfa leaves is not high enough to make a significant change in the methionine levels. Our preliminary data on rumen incubation experiments have demonstrated that the zeins are completely stable in the rumen of cows and thus qualify as the suitable rumen bypass protein that is rich in methionine. (C) 2003 Elsevier Ireland Ltd. All rights reserved.