CBSX3-Trxo-2 regulates ROS generation of mitochondrial complex II (succinate dehydrogenase) in Arabidopsis.

Despite being toxic at a high concentrations, reactive oxygen species (ROS) play a pivotal role as signaling molecules in responses to stress and regulation of plant development. The mitochondrial electron transport chain (ETC) is the major source of ROS in cells. Although the regulation of ROS in mitochondria has been well elucidated, the protein-protein interaction-based regulation of ETC members has not been well elucidated. In this study, we identified a CBS domain-containing protein, CBSX3, and found that CBSX3 activates o-type thioredoxin (Trx-o2) in mitochondria. In addition, we found that Trx-o2 interacts with SDH1, a subunit of ETC complex II. Knockdown (KD) of CBSX3 revealed anther indehiscence due to deficient lignin deposition caused by insufficient ROS accumulation, and increased expression of genes related to cell cycle and accelerated plant growth. However, in the CBSX3-overexpression plants, ROS accumulation increased, and cell cycle-related gene expression decreased, and thereby plant growth was retarded and leaf size decreased. Moreover, KD of CBSX3 and Trx-o2 conferred resistance to mitochondria ETC inhibitors in terms of ROS release. Taken together, we suggest that CBSX3-Trx-o2 is a ROS generation regulator of mitochondria in plants and plays an important role in regulating plant development and the redox system.