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. To address this issue, we generated mutants combining deficiencies in NTRC, 2-Cys Prx B, Trxs 1, and 4. The single and mutants showed a wild-type phenotype, growth retardation being noticed only in the double mutant. Moreover, the mutant displayed a more severe phenotype than the mutant, as shown by the impaired photosynthetic performance, altered chloroplast structure, and defective light-dependent reduction in the Calvin-Benson cycle and malate-valve enzymes. These effects were suppressed by the decreased contents of 2-Cys Prx, since the quadruple mutant displayed a wild-type-like phenotype. These results show that the activity of -type Trxs in the light-dependent regulation of biosynthetic enzymes and malate valve is controlled by the NTRC-2-Cys-Prx system.