Thioredoxin links redox to the regulation of fundamental processes of plant mitochondria
Résumé
Mitochondria contain thioredoxin (Trx), a regulatory disulfide protein,
and an associated flavoenzyme, NADPTrx reductase, which
provide a link to NADPH in the organelle. Unlike animal and yeast
counterparts, the function of Trx in plant mitochondria is largely
unknown. Accordingly, we have applied recently devised proteomic
approaches to identify soluble Trx-linked proteins in mitochondria
isolated from photosynthetic (pea and spinach leaves) and heterotrophic
(potato tubers) sources. Application of the mitochondrial
extracts to mutant Trx affinity columns in conjunction with proteomics
led to the identification of 50 potential Trx-linked proteins functional
in 12 processes: photorespiration, citric acid cycle and associated
reactions, lipid metabolism, electron transport, ATP synthesis
transformation, membrane transport, translation, protein assembly
folding, nitrogen metabolism, sulfur metabolism, hormone synthesis,
and stress-related reactions. Almost all of these targets were also
identified by a fluorescent gel electrophoresis procedure in which
reduction by Trx can be observed directly. Insomecases, the processes
targeted by Trx depended on the source of the mitochondria. The
results support the view that Trx acts as a sensor and enables
mitochondria to adjust key reactions in accord with prevailing redox
state. These and earlier findings further suggest that, by sensing
redox in chloroplasts and mitochondria, Trx enables the two organelles
of photosynthetic tissues to communicate by means of a
network of transportable metabolites such as dihydroxyacetone
phosphate, malate, and glycolate. In this way, light absorbed and
processed by means of chlorophyll can be perceived and function in
regulating fundamental mitochondrial processes akin to its mode of
action in chloroplasts.