Mitochondrial AtMTM1 and AtMTM2 are required for MnSOD activation,
stress response, and ion homeostasis
Abstract
Yeast manganese (Mn) trafficking transporter for mitochondrial
Mn-containing superoxide dismutase (MnSOD), yMTM1, belongs to
mitochondrial carrier family (MCF) and is crucial for yeast MnSOD
(ySOD2) activation. Arabidopsis AtMTM1 and AtMTM2 are homologs of yMTM1
and share conserved MCF motif sequence. We confirmed that AtMTM1 and
AtMTM2 interacted with AtMnSOD (AtMSD1) in mitochondria and recovered
ySOD2 activity in yMTM1-mutant cells. The redundant AtMTM1 and AtMTM2
have different gene expression patterns in tissues and methyl viologen
(MV)-induced oxidative stress and also responded to most metal stresses
along with AtMSD1. Bioassay revealed the contrasting root phenotype in
microRNA-mediated AtMTM1 mutant (mtm1-i) and AtMTM2-null mutant (mtm2)
under MV stress, and Mn supplement complemented the root lengths in
single and mtm1-i mtm2-double mutants. We found decreased MnSOD activity
was accompanied by increased FeSOD activity in double mutant. Transient
expression of chloroplast-destined AtMSD1 highlighted that unidentified
factors participated in AtMSD1 activation. Besides, the
exogenous-expressed AtMSD1 activity was decreased in double mutant, and
inductively coupled plasma optical emission spectrometry results showed
that AtMTM1 and AtMTM2 involved in Mn and Fe homeostasis with a
reciprocal regulation. Overall, AtMTM1 and AtMTM2 are important for
MnSOD metalation and ion homeostasis, and their physiological
regulations may stretch across mitochondria and chloroplasts.