Genetic manipulation of lysine catabolism in maize kernels

Abstract

In plants, lysine catabolism is thought to be controlled by a bifunctional enzyme, lysine ketoglutarate reductase/saccharopine dehydrogenase (LKR/SDH). Lysine is converted to saccharopine, through condensation with alpha-ketoglutarate, by LKR, and subsequently to glutamate and alpha-aminoadipate-delta-semialdehyde by SDH. To investigate lysine catabolism in maize kernels, we generated transgenic plants with suppressed LKR/SDH activity in either endosperm or embryo. We found that the suppression of LKR/SDH in endosperm induced an increase in free lysine in developing endosperm, which peaked at 32 days after pollination. At later stages of kernel development, most of the free lysine was found in the embryo along with an elevated level of saccharopine. By combining endosperm LKR/SDH suppression with embryo LKR/SDH suppression through crosses, the saccharopine level in embryo was reduced and resulted in higher lysine accumulation in mature kernels. These results reveal new insights into how free lysine level is regulated and distributed in developing maize kernels and demonstrate the possibility of engineering high lysine corn via the suppression of lysine catabolism.

Identification of the 2-Hydroxyglutarate and Isovaleryl-CoA Dehydrogenases as Alternative Electron Donors Linking Lysine Catabolism to the Electron Transport Chain ofArabidopsisMitochondria

“…In addition, numerous approaches have been taken to boost the Lys content in plants (Azevedo and Lea, 2001;Galili et al, 2001;Ufaz and Galili, 2008), and for this reason, the degradative pathway has also been targeted. In one such strategy, a series of transgenic maize (Zea mays) plants overaccumulating Lys were produced using distinct strategies, including an endosperm-specific RNA interference suppression of LKR/ SDH (Houmard et al, 2007;Frizzi et al, 2008;Reyes et al, 2009). Most approaches that led to accumulation of Lys also led to a concomitant degradation of Lys, resulting in the formation of saccharopine and a-aminoadipate d-semialdehyde (Falco et al, 1995;Houmard et al, 2007;Frizzi et al, 2008;Azevedo and Arruda, 2010).…”

Biotechnology for Enhanced Nutritional Quality in Plants

“…The combined approach of deregulating lysine synthesis and suppressing its catabolism was successful with as much as 4000 ppm free lysine accumulated in maize seeds. Reyes et al (2009) combined endospermspecific suppression of maize LKR/SDH with embryo-specific suppression of the gene, which resulted in a synergistic increase in maize seed free lysine content.…”

Genetic Enhancement of Grain Quality-Related Traits in Maize

“…These experiments showed that transgenic approaches, in addition to investigating relationships between zein synthesis and opaque endosperm, could be useful to increase kernel lysine content. Similarly, Reyes et al (2008), using RNAi, have produced transgenic maize lines that had LKR/SDH suppressed in the embryo, endosperm or both. These authors noted a synergist increase in free lysine content in the mature kernel when LKR/SDH was suppressed in both embryo and endosperm; these results have also suggested new insights into how free lysine level is regulated and distributed in developing grains.…”