Arabidopsis mTERF15 Is Required for Mitochondrial nad2 Intron 3 Splicing and Functional Complex I Activity

Abstract

Mitochondria play a pivotal role in most eukaryotic cells, as they are responsible for the generation of energy and diverse metabolic intermediates for many cellular events. During endosymbiosis, approximately 99% of the genes encoded by the mitochondrial genome were transferred into the host nucleus, and mitochondria import more than 1000 nuclear-encoded proteins from the cytosol to maintain structural integrity and fundamental functions, including DNA replication, mRNA transcription and RNA metabolism of dozens of mitochondrial genes. In metazoans, a family of nuclear-encoded proteins called the mitochondrial transcription termination factors (mTERFs) regulates mitochondrial transcription, including transcriptional termination and initiation, via their DNA-binding activities, and the dysfunction of individual mTERF members causes severe developmental defects. Arabidopsis thaliana and Oryza sativa contain 35 and 48 mTERFs, respectively, but the biological functions of only a few of these proteins have been explored. Here, we investigated the biological role and molecular mechanism of Arabidopsis mTERF15 in plant organelle metabolism using molecular genetics, cytological and biochemical approaches. The null homozygous T-DNA mutant of mTERF15, mterf15, was found to result in substantial retardation of both vegetative and reproductive development, which was fully complemented by the wild-type genomic sequence. Surprisingly, mitochondria-localized mTERF15 lacks obvious DNA-binding activity but processes mitochondrial nad2 intron 3 splicing through its RNA-binding ability. Impairment of this splicing event not only disrupted mitochondrial structure but also abolished the activity of mitochondrial respiratory chain complex I. These effects are in agreement with the severe phenotype of the mterf15 homozygous mutant. Our study suggests that Arabidopsis mTERF15 functions as a splicing factor for nad2 intron 3 splicing in mitochondria, which is essential for normal plant growth and development.

A Member of the Arabidopsis Mitochondrial Transcription Termination Factor Family Is Required for Maturation of Chloroplast Transfer RNAIle(GAU)

“…Hammani and Barkan (2014) suggest that other mTERFs, especially Arabidopsis BSM/RUG2, might execute similar functions. Indeed, in Arabidopsis mutants for the mitochondria-localized mTERF15 protein, splicing of nad2 intron 3 is significantly reduced (Hsu et al, 2014). However, our data indicate that the primary function of mTERF6 is not intron splicing ( Fig.…”

“…The maize BSM ortholog ZmmTERF4 is responsible for group II intron splicing, and this function in chloroplast RNA splicing might be conserved in BSM/RUG2 (Hammani and Barkan, 2014). In light of the role of BSM in chloroplast intron splicing (Hammani and Barkan, 2014), Hsu et al (2014) investigated splicing events in mitochondria from mterf15 plants. Indeed, their results strongly suggest that mTERF15 is also involved in intron splicing, namely splicing of intron 3 in the mitochondrial NADH dehydrogenase2 (nad2) transcript.…”

A Ribonucleoprotein Supercomplex Involved in trans-Splicing of Organelle Group II Introns

“…In most land plants, the genomes encode only a single OPR gene (33). However, interestingly, they exhibit tetratricopeptide repeat, pentatricopeptide repeat, and mTERF proteins, which also belong to the helical repeat superfamily and are involved in RNA processing (16,34,35), thereby demonstrating that despite the independent origin of group II introns in green algae and land plants, a co-evolution of helical repeat superfamily proteins as splicing factors has occurred.…”

The SLOW GROWTH3 Pentatricopeptide Repeat Protein Is Required for the Splicing of Mitochondrial NADH Dehydrogenase Subunit7 Intron 2 in Arabidopsis

“…What is This Factor 9, a Plant Organellar RNA Recognition domaincontaining protein, is required for rpl2 and ccmFc intron splicing . Arabidopsis mitochondrial transcriptional termination factor15 (mTERF15) is involved in the splicing of nad2 intron 3 (Hsu et al, 2014). Several nucleus-encoded maturases (e.g.…”