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Modification of lysine metabolism pathway in maize

Lysine belongs to the family of amino acids, which is not produced by monogastric animals and needs therefore to be supplied by their diet. Corn seeds, which are extensively, used as animal feed, have a limited amount in Lysine. Lysine, present at high levels is toxic to the plant cell and is therefore tightly regulated at its level of synthesis and/or degradation. DHPS is a key enzyme involved in lysine biosynthesis and is subjected to lysine feedback inhibition. Lysine keto-glutarate reductase (LKR) is the first enzyme participating in Lysine degradation. A mean to increase Lysine content in maize plants, is to over-express lysine insensitive versions of the DHPS gene (bacterial or mutated plant genes), and/or to decrease the production of LKR either by an anti-sense or RNAi approach aimed at down-regulating Lysine keto-glutarate reductase gene or by knocking out this gene via transposon insertion. Finally the over-produced lysine may be trapped into lysine-rich storage proteins, like a modified lysine-rich gamma Zein.

An increase in lysine (and methionine) was observed in mutated Arabidopsis DHPS over-expressing maize plants. LKR KO mutant lines were identified and introgressed into commercial type maize lines. The transposon insertions are located within the first intron of the gene. An increase in total lysine amounts was observed for those lines as it has been observed in Arabidopsis by G. Galili within this project. A commercial type maize hybrid has been produced and is in the process of being analysed.

Introduction of a proprietary modified lysine-rich gamma Zein (Biogemma Patent) gene into maize leads to increased total lysine content in the maize seeds. A depressed kernel phenotype has also been observed for the highest expressing line. It needs to be verified that this phenotype is linked to the presence of the modified lyine-rich gamma Zein.

Over-expression of a lysine insensitive DHPS gene in maize leads to increased total lysine amounts. A combination between this approach and the modified lysine-rich gamma Zein may have synergistical effects and further boost lysine concentration in maize seeds.

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