MISF2 Encodes an Essential Mitochondrial Splicing Cofactor Required for nad2 mRNA Processing and Embryo Development in Arabidopsis thaliana.

Tan-Trung Nguyen,Martine Quadrado,Hakim Mireau,Hagit Zer,Oren Ostersetzer-Biran,Michal Zmudjak,Ron Mizrahi,Corinne Best,Sofia Shevtsov

doi:10.3390/ijms23052670

Abstract

Mitochondria play key roles in cellular energy metabolism in eukaryotes. Mitochondria of most organisms contain their own genome and specific transcription and translation machineries. The expression of angiosperm mtDNA involves extensive RNA-processing steps, such as RNA trimming, editing, and the splicing of numerous group II-type introns. Pentatricopeptide repeat (PPR) proteins are key players in plant organelle gene expression and RNA metabolism. In the present analysis, we reveal the function of the MITOCHONDRIAL SPLICING FACTOR 2 gene (MISF2, AT3G22670) and show that it encodes a mitochondria-localized PPR protein that is crucial for early embryo development in Arabidopsis. Molecular characterization of embryo-rescued misf2 plantlets indicates that the splicing of nad2 intron 1, and thus respiratory complex I biogenesis, are strongly compromised. Moreover, the molecular function seems conserved between MISF2 protein in Arabidopsis and its orthologous gene (EMP10) in maize, suggesting that the ancestor of MISF2/EMP10 was recruited to function in nad2 processing before the monocot–dicot divergence ~200 million years ago. These data provide new insights into the function of nuclear-encoded factors in mitochondrial gene expression and respiratory chain biogenesis during plant embryo development.

Highlights

Mitochondria are key sites of cellular energy metabolism (i.e., ATP production), as well as of the biosynthesis of various essential metabolites
To better understand processes associated with mitochondrial RNA expression in plants, we assembled a collection of Arabidopsis T-DNA mutants affected in genes encoding mitochondria-targeted P-type Pentatricopeptide repeat (PPR) proteins and identified that heterozygous plants carrying insertions in the At3g22670 gene could not set homozygous mutants in their progeny
Domain search analysis using the PPR finder [50], PPRCODE [40], SMART [51] and CDD [52] algorithms indicated that the deduced product of AT3G22670 gene (Figures 1 and S1) encodes a 562 amino-acid PPR protein with a predicted topology of NH2-165-P-3-P-P-P-P-P-P-P-P-P-42-COOH (Figures 1 and S1a)

Summary

Introduction

Mitochondria are key sites of cellular energy metabolism (i.e., ATP production), as well as of the biosynthesis of various essential metabolites. CI is composed of more than 50 different subunits, 9 of which are encoded in the mitochondria (i.e., Nad, Nad, Nad, Nad, Nad4l, Nad, Nad, Nad, and Nad9) [4]. These are assembled into two main sub-domains known as the ‘membrane arm’ and ‘peripheral arm’ of the holo-CI enzyme [5]. The biogenesis of the respiratory chain machinery involves various mechanisms for regulating the expression of subunits that are encoded by two physically separate genetic compartments [3,6–8]. The identity of the factors and pathways involved in these regulations still await further analysis

Methods

Results

Discussion

Conclusion