LAUSR

Plant thioredoxins (Trxs) act as antioxidants and function as redox regulators in the chloroplast. Although the regulation of ROS in chloroplasts is well elucidated, the precise regulation mechanism of Trx remains unknown. Here, we characterize a novel chloroplast protein, Lon domain‐containing protein 1 (LCP1), which contains only a Lon domain, the precise function of which is not known. We find that LCP1 interacts with Trx‐y2 and represses its activity, and that knockdown (KD) of LCP1 causes anther indehiscence due to deficient lignin deposition. In addition, LCP1 KD plants show less ROS accumulation and lower expression of ROS‐responsive marker genes than the wild‐type plant. Taken together, we suggest that LCP1 directly regulates Trx‐y2 and controls H2O2 levels and, thereby, regulates lignin polymerization in the anther endothecium.