Phenotypes of mtm1-i and mtm2 mutants in adaption to long-term MV stress
Altered root elongation is an indicator of oxidative stress during plant development (Tsukagoshi, 2012). For long-term oxidative stress, we monitored the root growth of mtm1-i and mtm2 seedlings in various MV-containing plates for 5 to 15 d (Figure 8; Supplemental Figure S11) . The treatment period and MV concentration varied depending on the mutants.
In 8-d-old and 15-d-old seedlings, mtm1-i had significantly inhibited root growth compared with the WT under 10 to 30 nM MV treatments (Figure 8A; Supplemental Figure S11A, B) . In 10-d-old and 5-d-old seedlings, mtm2 had significantly longer root length than the WT under 1 to 10 nM MV treatments (Figure 8B; Supplemental Figure S11C) . Taken together, root lengths of 5 to 15-d-old mtm1-i and mtm2 seedlings showed the contrasting phenotypes compared with the WT under MV stress, implying redundantAtMTM1 and AtMTM2 genes have different responses toward oxidative stress.
Moreover, one-month-old mtm1-i and mtm2 plants both exhibited the early-flowering phenotypes compared with the WT under normal growth condition (Supplemental Figure S11D) , indicatingAtMTM1 and AtMTM2 play a role in this pathway.
Synergistic effects of AtMTM1 and AtMTM2 in mtm1-i mtm2-double mutants
In order to discover the synergistic effect of AtMTM1 andAtMTM2 genes, we crossed mtm1-i and mtm2 to generate the mtm1-i mtm2 -double mutant (Figure 9) .
Two stable lines of mtm1-i mtm2 -double mutant (#1 and#2 ) were screened and confirmed by qPCR (Figure 9A) , and the lowest expression line (#1 ) was focused. Six independent siblings of the mtm1-i mtm2-#1 revealed wobbling MnSOD and FeSOD activities (Figure 9B) . Compared with the WT, the relative SOD activity analysis in three siblings of mtm1-i mtm2-#1 showed the decreased MnSOD activity was accompanied by increased FeSOD activity(Figure 9C) . In addition, mtm1-i mtm2-#1 -double mutant retained the early-flowering phenotype compared with the WT(Figure 9D) and single mutants (Supplemental Figure S12) , indicating AtMTM1 and AtMTM2 have synergistic effects on MnSOD activity and early-flowering phenotype.