Overexpression of AtMTM1 and AtMTM2 had no effect on MnSOD activity
We overexpressed AtMTM1 and AtMTM2 with a CaMV35S promoter(Supplemental Figure S13) . Three independent lines ofAtMTM1 -overexpression (OE) and AtMTM2 -OE showed enhanced gene expressions by RT-PCR (Supplemental Figure S13A, B) . Nonetheless, MnSOD activity remained unchanged in AtMTM1 -OE andAtMTM2 -OE plants compared with the WT (Supplemental Figure S13C) , implying the saturated level of MnSOD activity retained in these overexpression lines as the WT.