AtMTM1 and AtMTM2 localize in mitochondria and interact with AtMnSOD (AtMSD1)
The subcellular localization of AtMTM1 and AtMTM2 was examined with a yellow fluorescent protein (YFP) fused to their C-terminal ends, and expressed in Arabidopsis protoplasts (Figure 1A) . The fluorescence signals of both AtMTM1-YFP and AtMTM2-YFP were merged well with MitoTracker, a mitochondria-specific dye. The results confirmed the presence of both proteins in mitochondria, as for yMTM1-green fluorescent protein (GFP) and AtMTM1-GFP in earlier reports (Luk et al., 2003; Su et al., 2007).
Bimolecular fluorescence complementation (BiFC) assay was conducted to examine protein-protein interactions among AtMTM1, AtMTM2, and AtMSD1(Figure 1B) . The reconstituted YFP signals revealed that AtMSD1 interacted with AtMTM1 and AtMTM2 independently, as well as the interaction of AtMTM1 and AtMTM2 (Supplemental Figure S2) , indicating AMTM1 and AtMTM2 contribute to AtMSD1 activity. Control experiments (Huang, Niu, Yang, & Jinn, 2016; Walter et al., 2004) were shown in Supplemental Figure S3 .