LAUSR

Photosynthesis involves a series of redox reactions and is the major source of reactive oxygen species in plant cells. Fluctuating light levels, which occur commonly in natural environments, affect photosynthesis; however, little is known about the specific effects of fluctuating light on the redox regulation of photosynthesis. Here, we performed global quantitative mapping of the Arabidopsis thaliana cysteine thiol redox proteome under constant light and fluctuating light conditions. We identified 8857 redox-switched thiols in 4350 proteins, and 1501 proteins that are differentially modified depending on light conditions. Notably, proteins related to photosynthesis, especially photosystem I (PSI), are operational thiol-switching hotspots. Exposure of wild-type A. thaliana to fluctuating light resulted in decreased PSI abundance, stability, and activity. Interestingly, in response to PSI photodamage, more of the PSI assembly factor PSA3 dynamically switches to the reduced state. Furthermore, the Cys199 and Cys200 sites in PSA3 are necessary for its full function. Moreover, thioredoxin m (Trx m) proteins play roles in redox switching of PSA3, and are required for PSI activity and photosynthesis. This study thus reveals a mechanism for redox-based regulation of PSI under fluctuating light, and provides insight into the dynamic acclimation of photosynthesis in a changing environment. This article is protected by copyright. All rights reserved.