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SUMMARY: We recently achieved targeted disruptions of cytoplasmic male sterility (CMS)‐associated genes in the mitochondrial genomes of rice and rapeseed by using mitochondria‐targeted transcription activator‐like effector nucleases (mitoTALENs). It was the first report of stable and heritable targeted gene modification of plant mitochondrial genomes. Here, we attempted to use mitoTALENs to disrupt two mitochondrial genes in the model plant Arabidopsis thaliana(Arabidopsis) using three different promoters and two types of TALENs. The targets were the two isoforms of the ATP synthase subunit 6 gene, atp6‐1 and atp6‐2. Each of these genes was successfully deleted and the mitochondrial genomes were recovered in a homoplasmic state. The nuclear genome also has a copy of atp6‐1, and we were able to confirm that it was the mitochondrial gene and not the nuclear pseudogene that was knocked out. Among the three mitoTALEN promoters tried, the RPS5A promoter was the most effective. Conventional mitoTALENs were more effective than single‐molecule mito‐compactTALENs. Targeted mitochondrial gene deletion was achieved by crossing as well as by floral‐dip transformation to introduce the mitoTALEN constructs into the nucleus. The gene disruptions were caused by large (kb‐size) deletions. The ends of the remaining sequences were connected to distant loci, mostly by illegitimate homologous recombinations between repeats. [ABSTRACT FROM AUTHOR]

Restorer-of-fertility ( Rf ) is a suppressor of cytoplasmic male sterility (CMS), a mitochondrion-encoded trait that has been reported in many plant species. The occurrence of CMS is considered to be independent in each lineage; hence, the question of how Rf evolved was raised. Sugar beet Rf resembles Oma1 , a gene for quality control of the mitochondrial inner membrane. Oma1 homologues comprise a small gene family in the sugar beet genome, unlike Arabidopsis and other eukaryotes. The sugar beet sequence that best matched Arabidopsis atOma1 was named bvOma1 ; sugar beet Rf ( RF1-Oma1 ) was another member. During anther development, atOma1 mRNA was detected from the tetrad to the microspore stages, whereas bvOma1 mRNA was detected at the microspore stage and RF1-Oma1 mRNA was detected during the meiosis and tetrad stages. A transgenic study revealed that, whereas RF1-Oma1 can bind to a CMS-specific protein and alter the higher-order structure of the CMS-specific protein complex, neither bvOma1 nor atOma1 show such activity. We favour the hypothesis that an ancestral Oma1 gene duplicated to form a small gene family, and that one of the copies evolved and acquired a novel expression pattern and protein function as an Rf , i.e. RF1-Oma1 evolved via neofunctionalization., Competing Interests: There are no competing interests., (© 2019 The Authors.)

The number, size and shape of polymorphic plant mitochondria are determined at least partially by mitochondrial fission. Arabidopsis mitochondria divide through the actions of a dynamin-related protein, DRP3A. Another plant-specific factor, ELM1, was previously shown to localize DRP3A to mitochondrial fission sites. Here, we report that mitochondrial fission is not completely blocked in the Arabidopsis elm1 mutant and that it is strongly manifested in response to cold treatment. Arabidopsis has an ELM1 paralogue ( ELM2 ) that seems to have only a limited role in mitochondrial fission in the elm1 mutant. Interestingly, cold-induced mitochondrial fragmentation was also observed in the wild-type, but not in a drp3a mutant, suggesting that cold-induced transient mitochondrial fragmentation requires DRP3A but not ELM1 or ELM2. DRP3A: GFP localized from the cytosol to mitochondrial fission sites without ELM1 after cold treatment. Together, these results suggest that Arabidopsis has a novel, cold-induced type of mitochondrial fission in which DRP3A localizes to mitochondrial fission sites without the involvement of ELM1 or ELM2., Competing Interests: The authors declare no conflict of interest.