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Gurdon, C, Maliga P.  2014.  Two distinct plastid genome configurations and unprecedented intraspecies length variation in the accD coding region in Medicago truncatula. DNA Reserach. 21:inpress. AbstractWebsite
We fully sequenced four and partially sequenced six additional plastid genomes of the model legume Medicago truncatula. Three accessions, Jemalong 2HA, Borung and Paraggio, belong to ssp. truncatula, and R108 to ssp. tricycla. We report here that the R108 ptDNA has a ∼45-kb inversion compared with the ptDNA in ssp. truncatula, mediated by a short, imperfect repeat. DNA gel blot analyses of seven additional ssp. tricycla accessions detected only one of the two alternative genome arrangements, represented by three and four accessions each. Furthermore, we found a variable number of repeats in the essential accD and ycf1 coding regions. The repeats within accD are recombinationally active, yielding variable-length insertions and deletions in the central part of the coding region. The length of ACCD was distinct in each of the 10 sequenced ecotypes, ranging between 650 and 796 amino acids. The repeats in the ycf1 coding region are also recombinationally active, yielding short indels in 10 regions of the reading frames. Thus, the plastid genome variability we report here could be linked to repeat-mediated genome rearrangements. However, the rate of recombination was sufficiently low, so that no heterogeneity of ptDNA could be observed in populations maintained by single-seed descent.
Gurdon, C, Svab Z, Feng Y, Kumar D, Maliga P.  2016.  Cell-to-cell movement of mitochondria in plants. Proc Natl Acad Sci U S A. 113:3395-400. AbstractWebsite
We report cell-to-cell movement of mitochondria through a graft junction. Mitochondrial movement was discovered in an experiment designed to select for chloroplast transfer fromNicotiana sylvestrisintoNicotiana tabacumcells. The alloplasmicN. tabacumline we used carriesNicotiana undulatacytoplasmic genomes, and its flowers are male sterile due to the foreign mitochondrial genome. Thus, rare mitochondrial DNA transfer fromN. sylvestristoN. tabacumcould be recognized by restoration of fertile flower anatomy. Analyses of the mitochondrial genomes revealed extensive recombination, tentatively linking male sterility toorf293, a mitochondrial gene causing homeotic conversion of anthers into petals. Demonstrating cell-to-cell movement of mitochondria reconstructs the evolutionary process of horizontal mitochondrial DNA transfer and enables modification of the mitochondrial genome by DNA transmitted from a sexually incompatible species. Conversion of anthers into petals is a visual marker that can be useful for mitochondrial transformation.