ACHT2 deactivates carbon assimilation during light-dark transition
In chloroplasts, photosynthetic efficiency relies on a delicate balance between reductive and oxidative thiol-based signaling networks. Members of the high-midpoint-potential atypical thioredoxins (Trxs) were shown to oxidize photosynthetic enzymes by channeling reducing equivalents to H2O2 through 2-Cys-Prx activity. However, it remains unclear which atypical-Trx isoforms regulate Calvin-Benson…
Photosynthetic efficiency in chloroplasts depends on a delicate balance between reductive and oxidative signaling networks. Atypical thioredoxins (Trxs) can oxidize photosynthetic enzymes, but it's unclear which isoforms regulate the Calvin-Benson cycle (CBC) during light-dark transitions. To investigate, researchers studied single, double, and triple mutant atypical Trx plants during dynamic light transitions.
They found that ACHT2 plays a key role in CBC inactivation during the dark-to-light transition. Acht2 plants showed a lower CBC inactivation state and alleviated redox-mediated bottlenecks in electron flow downstream of Fd, similar to plants lacking 2-Cys Prxs A and B (2cpab). However, mutations in ACHT1, ACHT4, or TrxL2 did not affect CBC inactivation.
Acht2 mutation itself did not harm plant fitness, but acht1/acht4 double mutant exhibited growth retardation, indicating severe phenotypes arise from oxidative regulation of other metabolic pathways by distinct atypical Trxs. These findings highlight the specific regulatory role of ACHT2 in the chloroplast oxidative network, offering insights into how activation-inactivation cycles aid plant adaptation to variable light conditions.
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