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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.

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]