Abstract
The tricarboxylic acid (TCA) cycle intermediate 2-oxoglutarate (2-OG) is used as an obligatory substrate in a range of oxidative reactions catalyzed by 2-OG-dependent dioxygenases. These enzymes are widespread in nature being involved in several important biochemical processes. We have recently demonstrated that tomato plants in which the TCA cycle enzyme 2-OG dehydrogenase (2-ODD) was antisense inhibited were characterized by early senescence and modified fruit ripening associated with differences in the levels of bioactive gibberellin (GA). Accordingly, there is now compelling evidence that the TCA cycle plays an important role in modulating the rate of flux from 2-OG to amino acid metabolism. Here we discuss recent advances in the biochemistry and molecular biology of 2-OG metabolism occurring in different biological systems indicating the importance of 2-OG and 2-OG dependent dioxygenases not only in glucosinolate, flavonoid and alkaloid metabolism but also in GA and amino acid metabolism. We additionally summarize recent findings regarding the impact of modification of 2-OG metabolism on biosynthetic pathways involving 2-ODDs.
Highlights
SUMMARY In summary, 2-OG is a TCA cycle intermediate and a co-factor for a diverse range of enzymes involved in amino acid, glucosinolate, flavonoid, alkaloid, and GA metabolism
In the case of GA and amino acid, recent evidence indicates that 2-OG levels control the rate of their biosynthesis
Whilst preliminary studies have been attempted to understand evolutionary origins of the 2-ODD, more comprehensive analysis of this will be required to deepen our understanding of this important gene family
Summary
Several 2-ODDs are involved in the synthesis of different alkaloids, which is the second largest class of plant secondary metabolism, have been characterized in several plant species. In the biosynthesis of tropane alkaloid, hyoscyamine 6-hydroxylase (H6H) in scoporamine biosynthesis of Hyoscyamus niger (Figure 2D; Matsuda et al, 1991), Anisodus tanguticus (Liu et al, 2005), and Atropa belladonna (Suzuki et al, 1999), 2 -deoxymugineic-acid 2 -dioxygenase (IDS3) in mugineic acid biosynthesis of Hordeum vulgare (Nakanishi et al, 2000) have been characterized.
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