The ferredoxin/thioredoxin pathway constitutes an indispensable redox-signaling cascade for light-dependent reduction of chloroplast stromal proteins

• Published in: The Journal of biological chemistry Vol. 298; no. 12; p. 102650
• Main Authors: Yoshida, Keisuke, Yokochi, Yuichi, Tanaka, Kan, Hisabori, Toru
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-12-2022; American Society for Biochemistry and Molecular Biology
• Subjects: Arabidopsis - metabolism; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; Chloroplast Proteins - metabolism; Chloroplasts - metabolism; CRISPR/Cas9; Ferredoxins - genetics; Ferredoxins - metabolism; ferredoxin–thioredoxin reductase; Oxidation-Reduction; Photosynthesis; redox regulation; thioredoxin; Thioredoxins - metabolism; redox regulation; CF1-γATP synthase; CRISPR/Cas9; FBPase; thioredoxin; FTR; PRK; 2-Cys Prx; Arabidopsis thaliana; MDH; RCA; NTRC; ferredoxin–thioredoxin reductase; SBPase; Trx; GAPDH; Fd; FTRc
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/j.jbc.2022.102650

To ensure efficient photosynthesis, chloroplast proteins need to be flexibly regulated under fluctuating light conditions. Thiol-based redox regulation plays a key role in reductively activating several chloroplast proteins in a light-dependent manner. The ferredoxin (Fd)/thioredoxin (Trx) pathway has long been recognized as the machinery that transfers reducing power generated by photosynthetic electron transport reactions to redox-sensitive target proteins; however, its biological importance remains unclear, because the complete disruption of the Fd/Trx pathway in plants has been unsuccessful to date. Especially, recent identifications of multiple redox-related factors in chloroplasts, as represented by the NADPH–Trx reductase C, have raised a controversial proposal that other redox pathways work redundantly with the Fd/Trx pathway. To address these issues directly, we used CRISPR/Cas9 gene editing to create Arabidopsis mutant plants in which the activity of the Fd/Trx pathway was completely defective. The mutants generated showed severe growth inhibition. Importantly, these mutants almost entirely lost the ability to reduce several redox-sensitive proteins in chloroplast stroma, including four Calvin–Benson cycle enzymes, NADP–malate dehydrogenase, and Rubisco activase, under light conditions. These striking phenotypes were further accompanied by abnormally developed chloroplasts and a drastic decline in photosynthetic efficiency. These results indicate that the Fd/Trx pathway is indispensable for the light-responsive activation of diverse stromal proteins and photoautotrophic growth of plants. Our data also suggest that the ATP synthase is exceptionally reduced by other pathways in a redundant manner. This study provides an important insight into how the chloroplast redox-regulatory system operates in vivo.