Thioredoxin 2 and 1 Show Different Subcellular Localizations and Redox-Active Functions, and Are Extrachloroplastic Factors Influencing Photosynthetic Performance in Fluctuating Light.

Arabidopsis contains eight different -type thioredoxins (Trx) being distributed in different cell organelles. Although Trx 2 is deemed to be confined to mitochondria, its subcellular localization and function are discussed controversially. Here, cell fractionation studies were used to clarify this question, showing Trx 2 protein to be exclusively localized in microsomes rather than mitochondria. Furthermore, Arabidopsis , and mutants were analyzed to compare the role of Trx 2 with mitochondrial Trx 1. Under medium light, and showed impaired growth, while was similar to wild type. In line with this, and clustered differently from wild type with respect to nocturnal metabolite profiles, revealing a decrease in ascorbate and glutathione redox states. Under fluctuating light, these genotypic differences were attenuated. Instead, the double mutant showed an improved NADPH redox balance, compared to wild type, accompanied by increased photosynthetic efficiency, specifically in the high-light phases. Conclusively, Trx 2 and Trx 1 are differentially localized in microsomes and mitochondria, respectively, which is associated with different redox-active functions and effects on plant growth in constant light, while there is a joint role of both Trxs in regulating NADPH redox balance and photosynthetic performance in fluctuating light.