The Functional Relationship between NADPH Thioredoxin Reductase C, 2-Cys Peroxiredoxins, and -Type Thioredoxins in the Regulation of Calvin-Benson Cycle and Malate-Valve Enzymes in Arabidopsis.

The concerted regulation of chloroplast biosynthetic pathways and NADPH extrusion via malate valve depends on and thioredoxins (Trxs). The finding that decreased levels of the thiol-peroxidase 2-Cys peroxiredoxin (Prx) suppress the severe phenotype of Arabidopsis mutants lacking NADPH-dependent Trx reductase C (NTRC) and Trxs uncovered the central function of the NTRC-2-Cys-Prx redox system in chloroplast performance. These results suggest that Trxs are also regulated by this system; however, the functional relationship between NTRC, 2-Cys Prxs, and type Trxs is unknown.

Exploring the Functional Relationship between -Type Thioredoxins and 2-Cys Peroxiredoxins in Chloroplasts.

Thioredoxins (Trxs) are small, ubiquitous enzymes that catalyze disulphide-dithiol interchange in target enzymes. The large set of chloroplast Trxs, including , , and subtypes, use reducing equivalents fueled by photoreduced ferredoxin (Fdx) for fine-tuning photosynthetic performance and metabolism through the control of the activity of redox-sensitive proteins. Although biochemical analyses suggested functional diversity of chloroplast Trxs, genetic studies have established that deficiency in a particular Trx subtype has subtle phenotypic effects, leading to the proposal that the Trx isoforms are functionally redundant.

Insights into the function of NADPH thioredoxin reductase C (NTRC) based on identification of NTRC-interacting proteins in vivo.

Redox regulation in heterotrophic organisms relies on NADPH, thioredoxins (TRXs), and an NADPH-dependent TRX reductase (NTR). In contrast, chloroplasts harbor two redox systems, one that uses photoreduced ferredoxin (Fd), an Fd-dependent TRX reductase (FTR), and TRXs, which links redox regulation to light, and NTRC, which allows the use of NADPH for redox regulation. It has been shown that NTRC-dependent regulation of 2-Cys peroxiredoxin (PRX) is critical for optimal function of the photosynthetic apparatus.

Chloroplast Redox Regulatory Mechanisms in Plant Adaptation to Light and Darkness.

Light is probably the most important environmental stimulus for plant development. As sessile organisms, plants have developed regulatory mechanisms that allow the rapid adaptation of their metabolism to changes in light availability. Redox regulation based on disulfide-dithiol exchange constitutes a rapid and reversible post-translational modification, which affects protein conformation and activity.