Significance of AtMTM1 and AtMTM2 for Mitochondrial MnSOD Activation in Arabidopsis.

Shu-Hsuan Hu,Shu-Fan Lin,Wen-Yu Kuo,Tsung-Luo Jinn,Chien-Hsun Huang,Ya-Chen Huang

doi:10.3389/fpls.2021.690064

Abstract

The manganese (Mn) tracking factor for mitochondrial Mn superoxide dismutase (MnSOD) has been annotated as yMTM1 in yeast, which belongs to the mitochondrial carrier family. We confirmed that Arabidopsis AtMTM1 and AtMTM2 are functional homologs of yMTM1 as they can revive yeast MnSOD activity in yMTM1-mutant cells. Transient expression of AtMnSOD-3xFLAG in the AtMTM1 and AtMTM2-double mutant protoplasts confirmed that AtMTM1 and AtMTM2 are required for AtMnSOD activation. Our study revealed that AtMnSOD interacts with AtMTM1 and AtMTM2 in the mitochondria. The expression levels of AtMTM1, AtMTM2, and AtMnSOD respond positively to methyl viologen (MV) and metal stress. AtMTM1 and AtMTM2 are involved in Mn and Fe homeostasis, root length, and flowering time. Transient expression of chloroplast-destined AtMnSOD revealed that an evolutionarily conserved activation mechanism, like the chloroplastic-localized MnSOD in some algae, still exists in Arabidopsis chloroplasts. This study strengthens the proposition that AtMTM1 and AtMTM2 participate in the AtMnSOD activation and ion homeostasis.

Highlights

Cellular reactive oxygen species (ROS) contain superoxide anion radicals, hydroxyl radicals, singlet oxygen, and hydrogen peroxide, whose generation is induced by high light intensity, heat, drought, and salt stress
We demonstrated that AtMTM1 and AtMTM2 are necessary for AtMnSOD activation by using transient expression assay (Figure 3)
We confirmed that AtMTM1 and AtMTM2 interact with AtMnSOD in mitochondria by using the bimolecular fluorescence complementation (BiFC) assay (Figure 4), which agrees with the proteomic evidence of mitochondrial AtMTM1 and AtMTM2 (Senkler et al, 2017)

Summary

Introduction

Cellular reactive oxygen species (ROS) contain superoxide anion radicals, hydroxyl radicals, singlet oxygen, and hydrogen peroxide, whose generation is induced by high light intensity, heat, drought, and salt stress. Superoxide anion radicals are mainly generated from the respiratory and photosynthetic electron transport chains in the mitochondria and chloroplasts and can rapidly damage nearby cell components. The superoxide dismutases (SODs) catalyze the conversion of toxic superoxide anion radicals to oxygen and hydrogen peroxide; the corresponding cofactors in SODs are transition metal ions that accept or donate an electron during the dismutation process (Fridovich, 1975; Halliwell, 1994; Apel and Hirt, 2004). Superoxide dismutases are classified as CuZnSOD, FeSOD, Mn superoxide dismutase (MnSOD), or NiSOD based on their metal cofactors. These metalloenzymes are important for cell survival under oxidative stress (Bowler et al, 1994). NiSOD is present in Streptomyces and cyanobacteria (Choudhury et al, 1999; Barondeau et al, 2004; Priya et al, 2007)

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