A T-DNA insertion knockout of the bifunctional lysine-ketoglutarate reductase/saccharopine dehydrogenase gene elevates lysine levels in arabidopsis seeds

Plants possess both anabolic and catabolic pathways for the essential amino acid lysine (Lys). However, although the biosynthetic pathway was clearly shown to regulate Lys accumulation in plants, the functional significance o f Lys catabolism has not been experimentally elucidated. To address this is sue, we have isolated an Arabidopsis knockout mutant with a T-DNA inserted into exon 13 of the gene encoding Lys ketoglutarate reductase/saccharopine dehydrogenase. This bifunctional enzyme controls the first two steps of Lys catabolism. The phenotype of the LKR/SDH knockout was indistinguishable fr om wild-type plants under normal growth conditions, suggesting that Lys cat abolism is not an essential pathway under standard growth conditions. Howev er, mature seeds of the knockout mutant over-accumulated Lys compared with wild-type plants. This report provides the first direct evidence for the fu nctional significance of Lys catabolism in regulating Lys accumulation in s eeds. Such a knockout mutant may also provide new perspectives to improve t he level of the essential amino acid Lys in plant seeds.