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IN BRIEF

Mitochondrial Recombination Surveillance

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The plant mitochondrial genome is highly recombinogenic, and rearrangements often occur in tissue culture conditions, during wide hybridization events, or as spontaneous events. Mitochondrial genomic rearrangement is often detected as the induction or loss of cytoplasmic male sterility (CMS). A number of substoichiometric DNA intermediates are retained over multiple generations within the mitochondrial population, and a phenomenon called substoichiometric shifting (SSS) has been observed, which is characterized by the amplification or suppression of specific subgenomic molecules under certain conditions. SSS is influenced by nuclear gene expression and alters the expression of genes (including CMS mutations) encoded in the subgenomic intermediates. Shedge et al. (pages 1251–1264) investigate two genes associated with SSS in Arabidopsis. MSH1 and RECA3 encode homologs of E. coli MutS mismatch repair component and RecA protein, respectively, and mutations at either locus result in SSS. The authors find that RECA3 and MSH1 are uniquely adapted in plants to control mitochondrial genome maintenance. The expression of both genes is low in most plant tissues but enhanced during flower development, when SSS likely occurs. The SSS process appears to be associated with nuclear regulation of de novo mitochondrial nonhomologous recombination initiated by double-strand breaks. RECA3 and MSH1 are postulated to be part of a surveillance mechanism that directs conversion events between short repeats while allowing recombination-dependent replication to be initiated at long repeats. recA3 or msh1 mutations render the recombination surveillance system nonfunctional, shifting the stoichiometry of various segments of the genome, and these events in the mutants resemble low-frequency, sporadic events that result in SSS and CMS in wild populations.

View larger version (88K): [in this window] [in a new window] [as a PowerPoint slide]   Abnormal flower morphology of recA3 msh1 double mutant plants in which the stigma matures before the pollen, and fewer pollen grains are present than in the wild type.

www.plantcell.org/cgi/doi/10.1105/tpc.107.190410

Related articles in Plant Cell:

Plant Mitochondrial Recombination Surveillance Requires Unusual RecA and MutS Homologs

Vikas Shedge, Maria Arrieta-Montiel, Alan C. Christensen, and Sally A. Mackenzie
Plant Cell 2007 19: 1251-1264. [Abstract] [Full Text]  

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