Characterization of Arabidopsis mtm1, mtm1-i, andmtm2 mutant lines
To investigate the physiological functions of AtMTM1 andAtMTM2 , we characterized T-DNA insertion mutants of mtm1-1and -2 , and microRNA-mediated AtMTM1- mutant (mtm1-i ) lines (Supplemental Figures S8, 9) . Besides, homozygous T-DNA insertion lines of mtm2-1 , -2 , and-3 were analyzed (Supplemental Figure S10) .
In mtm1-1 and -2 mutants, T-DNA is inserted in the 3’-UTR and 5’-UTR of the AtMTM1 gene, respectively (Supplemental Figure S8A) . Homozygous lines were confirmed by genotyping. RT-PCR and qPCR revealed both mtm1-1 and -2 are knock-down mutants, and the mtm1-1 is a 45% knock-down mutant compared with the WT(Supplemental Figure S8B) .
We screened five stable T4 lines of mtm1-i mutant(Supplemental Figure S9A) , and the two lowest expression lines remained about 20% AtMTM1 expression (Supplemental Figure S9B, mtm1-i-3 and -5) . The mtm1-i-3 mutant remained unaffected MnSOD and FeSOD activities compared with the WT(Supplemental Figure S9C) .
In mtm2-1 mutant, T-DNA is inserted in the last exon of theAtMTM2 coding region (Supplemental Figure S10A) . Genotyping, RT-PCR, and qPCR confirmed mtm2-1 is a null mutant. MnSOD and FeSOD activities in mtm2-1 are similar to the WT(Supplemental Figure S10B) . In mtm2-2 and -3mutants, T-DNA is inserted in the intron, but RT-PCR assay showed the expression of AtMTM2 was not majorly affected(Supplemental Figs. S10A, C) .
In the following study, we examined the redundant function and synergistic effect of AtMTM1 and AtMTM2 by usingmtm1-i-3 (referred as mtm1-i ) and mtm2-1 (referred as mtm2 ) mutants.