Reduced levels of NADH-dependent glutamate dehydrogenase decrease the glutamate content of ripe tomato fruit but have no effect on green fruit or leaf

FERRARO GISELA; D'ANGELO MATILDE; SULPICE RONAN; STITT MARK; VALLE ESTELA

JOURNAL OF EXPERIMENTAL BOTANY

OXFORD UNIV PRESS

Lugar: Oxford; Año: 2015 vol. 66 p. 3381 - 3389

0022-0957

Glutamate is a taste enhancer that contributes to the characteristic flavor of foods. In tomato fruit, the glutamate content increases dramatically during the ripening process, becoming the most abundant free amino acid in red tomato fruit. There is also a concomitant increase in NADH-dependent glutamate dehydrogenase (GDH) activity during the ripening transition. This enzyme is located in the mitochondria and catalyzes the reversible amination of 2-oxoglutarate to glutamate. To investigate the potential effect of GDH on glutamate metabolism, the abundance of GDH was altered by artificial microRNA technology. Efficient silencing of all the endogenous SlGDH genes was achieved, leading to a dramatic decrease in total GDH activity. This decrease in GDH activity did not lead to any clear morphological or metabolic phenotype in leaves or green fruit. However, red fruit on the transgenic plants showed markedly reduced levels of the glutamate and a large increase in the content of aspartate, glucose and fructose in comparison to wild-type fruit. These results suggest that GDH is involved in the synthesis of Glu in tomato fruit during the ripening processes. This contrasts with the biological role ascribed to GDH in many other tissues and species. Overall, these findings suggest that GDH has a major effecton the control of metabolic composition during tomato fruit ripening,but not at other stages of development.