Novel composition of mitochondrial genomes in Petunia somatic hybrids derived from cytoplasmic male sterile and fertile plants

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 from Nicotiana sylvestris into Nicotiana tabacum cells. The alloplasmic N. tabacum line we used carries Nicotiana undulata cytoplasmic genomes, and its flowers are male sterile due to the foreign mitochondrial genome. Thus, rare mitochondrial DNA transfer from N. sylvestris to N. tabacum could be recognized by restoration of fertile flower anatomy. Analyses of the mitochondrial genomes revealed extensive recombination, tentatively linking male sterility to orf293, 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.

Section: Discussionmentioning

confidence: 90%

Cell-to-cell movement of mitochondria in plants

Gurdon

Sváb

Feng

et al. 2016

“…Mitochondria in plant cells may participate in a massive fusion cycle (28), and recombination of mtDNA following mitochondrial fusion is well documented (see, for example, ref. 29). Cotransfer of mtDNA and ptDNA in earlier studies may have been missed because of limited probing, or because it does not occur in all species combinations.…”

Section: Discussionmentioning

confidence: 98%

Exceptional transmission of plastids and mitochondria from the transplastomic pollen parent and its impact on transgene containment

Sváb

Maliga

2007

153

108

Plastids in Nicotiana tabacum are normally transmitted to the progeny by the maternal parent only. However, low-frequency paternal plastid transmission has been reported in crosses involving parents with an alien cytoplasm. Our objective was to determine whether paternal plastids are transmitted in crosses between parents with the normal cytoplasm. The transplastomic father lines carried a spectinomycin resistance (aadA) transgene incorporated in the plastid genome. The mother lines in the crosses were either (i) alloplasmic, with the Nicotiana undulata cytoplasm that confers cytoplasmic male sterility (CMS92) or (ii) normal, with the fertile N. tabacum cytoplasm. Here we report that plastids from the transplastomic father were transmitted in both cases at low (10 ؊4 -10 ؊5 ) frequencies; therefore, rare paternal pollen transmission is not simply due to breakdown of normal controls caused by the alien cytoplasm. Furthermore, we have found that the entire plastid genome was transmitted by pollen rather than small plastid genome (ptDNA) fragments. Interestingly, the plants, which inherited paternal plastids, also carried paternal mitochondrial DNA, indicating cotransmission of plastids and mitochondria in the same pollen. The detection of rare paternal plastid transmission described here was facilitated by direct selection for the transplastomic spectinomycin resistance marker in tissue culture; therefore, recovery of rare paternal plastids in the germline is less likely to occur under field conditions. Nicotiana tabacum ͉ organelle inheritance ͉ plastid transformation ͉ pollen transmission D NA in a plant cell is found in three cellular compartments: the nucleus, plastids, and mitochondria. Genes encoded in the nucleus are inherited biparentally, according to Mendel's rules. In contrast, plastids and mitochondria may be inherited maternally, paternally, or from both parents. In most crops, the maternal parent transmits plastids, because plastids are excluded from the sperm cell or, even if not excluded, are left behind in synergid cells during fertilization (1-3). In Chlamydomonas reinhardtii, a unicellular alga, in which maternal (mating-type ϩ ) and paternal (mating-type Ϫ ) chloroplasts fuse, only the maternal plastid genome (ptDNA) is inherited, because the maternal ptDNA is protected by methylation, whereas the nonmethylated paternal ptDNA is degraded (4). Once protocols for plastid transformation were developed (5, 6), localization of transgenes in the plastid genome was advocated as a means of transgene containment (7). Utility of plastid localization for containment became a hotly debated issue when the first herbicide-resistant transplastomic plants were obtained (8, 9). The reason for skepticism was the reported relatively high-frequency paternal ptDNA transmission in species in which plastids were assumed to be inherited strictly by the maternal parent. Paternal ptDNA transmission was detected in crosses by using streptomycin resistance (in 0.07-2.5%) (10, 11) and tentoxin resistance (0.5-2.5%) (12) in...

“…Moreover, Wildman et al, (28) observed various physical interactions between the two organelles in cinematic studies of living cells. Membrane continuities might facilitate intermolecular recombination; evidence for both intermolecular and intramolecular recombination has been accumulated for both mtDNA (1,(29)(30)(31)(32) and ctDNA (33,34 Biochemistry: Stem and Palmer Biochemistry: Stern and Palmer ctDNA sequences quite unlikely to have a function in the mitochondrion: rbcL (corn) and the ctDNA ribosoinal RNA genes (corn and pea). It has been suggested that sequences from within the ctDNA inverted repeat might play a functional role within the corn mitochondrial genome because alterations in this ctDNA-homologous sequence are observed in the mtDNA of cytoplasmic male sterile corn (6).…”

Section: Discussionmentioning

confidence: 99%

“…It has been suggested that sequences from within the ctDNA inverted repeat might play a functional role within the corn mitochondrial genome because alterations in this ctDNA-homologous sequence are observed in the mtDNA of cytoplasmic male sterile corn (6). However, these alterations now appear to represent only a small fraction of the numerous rearrangements that distinguish fertile and male-sterile mtDNAs in both corn (38) and petunia (32) and, thus, are probably unrelated causally to the expression of male sterility. We feel that the widespread presence of ctDNA sequences in plant mtDNA is best regarded as a dramatic demonstration of the dynamic nature of interactions between the chloroplast and the mitochondrion, similar to the ongoing process of interorganellar DNA transfer already documented between mitochondrion and nucleus (39)(40)(41)(42)(43) and between chloroplast and nucleus (44).…”

Section: Discussionmentioning

confidence: 99%

Extensive and widespread homologies between mitochondrial DNA and chloroplast DNA in plants

Stern

Palmer

1984

170

We used hybridization techniques to demonstrate that numerous sequence homologies exist between cloned mung bean and spinach chloroplast DNA (ctDNA) restriction fragments and mtDNAs from corn, mung bean, spinach, and pea. The strongest cross-homologies are between clones derived from the ctDNA inverted repeat and mtDNA from corn and pea, although all the ctDNA clones tested hybridized to at least one mtDNA restriction fragment. Known chloroplast genes showing strong mtDNA homologies include those for the large subunit of ribulosebisphosphate carboxylase, which hybridizes to corn mtDNA, and the 13 subunit of the chloroplast ATPase, which hybridizes to mung bean mtDNA. Certain of these homologies were confirmed by using cloned spinach mtDNA restriction fragments as probes in reciprocal hybridizations to ctDNA. Several of these ctDNA-homologous mtDNA sequences were shown to be much more closely related to ctDNA from the same species than to that of a distantly related species. We interpret these differential homologies as evidence for relatively recent DNA sequence transfer events, suggesting that transposition between the two genomes is an ongoing evolutionary process.The mitochondrial genomes of higher plants are large in comparison to their fungal and mammalian counterparts, varying from 218 kilobase pairs (kb) in the genus Brassica (1) to an estimated 2400 kb in muskmelon (2). In contrast, chloroplast genomes are highly conserved in size (120-180 kb) and in sequence arrangement (3). To date, no correlation has been demonstrated between mitochondrial genome size and the number of polypeptide products made by isolated mitochondria. It seems likely, therefore, that higher plant mtDNA consists largely of noncoding sequences (2,4,5).Following the observation that corn mtDNA contains a 12-kb segment of the corn chloroplast DNA (ctDNA) inverted repeat (6), we wished to ascertain whether this phenomenon is restricted to corn or if it is a feature of other plant taxa. Here we present hybridization studies that extend these earlier results and demonstrate the widespread presence of ctDNA sequences in the mitochondrial genomes of four diverse species of angiosperms. MATERIALS AND METHODSMitochondria were prepared from 1-wk-old dark-grown pea (Pisum sativum cv. Alaska), mung bean (Vigna radiata cv. berken), and corn (Zea mays B37-N) seedlings and from green spinach (Spinacia oleracea) leaves by treating mitochondria with DNase I by the method of Kolodner and Tewari (7). Chloroplasts were prepared either by the DNase I procedure (8) or by sucrose gradient centrifugation (9). DNAs were prepared from the purified, lysed organelles by two rounds of CsCl-ethidium bromide equilibrium centrifugation (9). Restriction endonuclease digestions, agarose gel electrophoresis, preparation of nitrocellulose filters, nicktranslations, and hybridizations were carried out as described (9). All filters were washed in 0.3 M NaCl/30 mM trisodium citrate/0.1% sodium dodecyl sulfate at 650C. Recombinant clones of spinach mtDNA were cons...