Type Of Male Sterility Research Articles

Cytological and mapping analysis of a novel male sterile type resulting from spontaneous floral organ homeotic conversion in marigold (Tagetes erecta L.)

A male sterile line was isolated in marigold (Tagetes erecta L.) and cytological analysis determined this to be a novel genic male sterility trait (Tems). Through the use of amplified fragment length polymorphisms (AFLPs) and bulked segregant analysis (BSA), tightly linked markers of Tems were identified with a view towards a map-based cloning strategy. It was found that spontaneous homeotic conversion of floral organs was the underlying cause of the male sterility in this marigold line. Thus, petals of male sterile plants resembled sepal-like structures and the stamens were partially converted to styles, although without the full characteristics or function of the true style organs. We have constructed a fine marker-based map for the Tems gene. This is intended to provide a tool for marker assisted selection (MAS) strategies in hybrid breeding and map-based cloning strategies for the male sterility locus. We discuss the significance of this spontaneously derived genic male sterility trait relating to the homeotic conversion of floral organs in marigold.

Directional transduction of male sterile gene rfv 1 of NIAN type in wheat

A new method for producing a NIAN type wheat maintenance line with the male sterile gene rfv 1 was described. That is the variety Xinong Fp1, a 1BL/1RS translocation line, as the acceptor and Triticum macha var. subletschchumicum, a non-1BL/1RS translocation line, as the donor, a directional substitution backcross was made and confirmed by chromosome of root tip preparations and SDS-PAGE analysis. The male sterile gene rfv 1 of Triticum macha var. subletschchumicum was transferred to the genome of Xinong Fp1. A new NIAN type wheat maintenance line with the male sterile gene rfv 1 was bred. The method described was successful in breeding a new male sterile type for hybrid wheat production.

Determining the plasmotypic structure of rye populations by SCAR markers

In rye (Secale cereale L.), 2 types of cytoplasmic male sterility are known: Pampa type (CMS-P) and Vavilovii type (CMS-V). As an alternative method to the conventional plasmotype-genotype interaction test, for identification of the cytoplasm type, the use of sequence-characterised amplified region (SCAR) markers was validated in this study. In over 2600 individual rye plants, representing 26 populations originating from Poland (18 cultivars), Iran (5 populations of primitive rye), and South America (3 populations), the cytoplasm type was determined by using a set of 3 SCAR markers. For about 10% of these individuals, the plasmotype-genotype interaction test was performed in parallel. The results of both tests were fully consistent. In the majority of the Polish populations, CMS-V was present, and only 4 populations contained CMS-P. Primitive Iranian populations contained predominantly normal cytoplasm, and only occasionally CMS-P was identified in them. South American populations displayed a mixture of normal cytoplasm, CMS-P and CMS-V. This work validates the use of SCAR markers as a reliable and quick method to determine the plasmotypic diversity of rye populations on a large scale.

Genetic analysis of fertility-restorer genes in rice

Wild-abortive (WA), Honglian (HL) and Baro-II (BT) are three important cytoplasmic male sterility (CMS) types in rice. It is essential to investigate genetic mode and allelism of fertility restorer (Rf) genes and the relationship between Rf and CMS. Fertility of the all test-cross F1 plants shows that the restorer-maintainer relationship is similar for HL-CMS and BT-CMS, while that is variance for WA-CMS and HL-CMS (or BT-CMS), respectively. Genetic analysis of Rf genes indicates that HL-or BT-CMS are controlled by single dominant Rf gene and WA-CMS is controlled by one or two pairs of dominant Rf genes, which reflects the characters of the gametophytic and sporophytic restoration CMS type. It is concluded that there are at least three Rf loci in different accessions with Rf genes for each CMS type.

Inhibition of chalcone synthase Expression in Anthers of Raphanus sativus with Ogura Male Sterile Cytoplasm

Expression of the mitochondrial gene orf138 causes Ogura cytoplasmic male sterility (CMS) in Raphanus sativus, but little is known about the mechanism by which CMS takes place. A preliminary microarray experiment revealed that several nuclear genes concerned with flavonoid biosynthesis were inhibited in the male-sterile phenotype. In particular, a gene for one of the key enzymes for flavonoid biosynthesis, chalcone synthase (CHS), was strongly inhibited. A few reports have suggested that the inhibition of CHS causes nuclear-dependent male sterile expression; however, there do not appear to be any reports elucidating the effect of CHS on CMS expression. In this study, the expression patterns of the early genes in the flavonoid biosynthesis pathway, including CHS, were investigated in normal and male-sterile lines. In order to determine the aberrant stage for CMS expression, the characteristics of male-sterile anthers are observed using light and transmission electron microscopy for several stages of flower buds. The expression of CHS and the other flavonoid biosynthetic genes in the anthers were compared between normal and male-sterile types using real time RT-PCR. Among the flavonoid biosynthetic genes analysed, the expression of CHS was strongly inhibited in the later stages of anther development in sterility cytoplasm; accumulation of putative naringenin derivatives was also inhibited. These results show that flavonoids play an important role in the development of functional pollen, not only in nuclear-dependent male sterility, but also in CMS.

A new fertility restorer locus linked closely to the Rfo locus for cytoplasmic male sterility in radish

In this study, we have investigated a new fertility restorer (Rf) locus for cytoplasmic male sterility (CMS) in radish. We have obtained a CMS-Rf system consisting of sterile line '9802A1', maintainer line '9802B1' and restorer line '9802H'. F(1) plants from cross between sterile line '9802A1' and restorer line '9802H' were all male fertile, self pollination of F(1) plants produced an F(2) segregating population consisting of 600 individuals. The segregating population was found to fit a segregation ratio 3:1 for male fertile and sterile types, indicating that male fertility is restored by a single dominant gene (termed Rfo2) in the CMS-Rf system. Based on the DNA sequence of Rfo/Rfk1 (AJ535623), just one full length gene in the sterile line '9802A1', in the restorer line '9802H' and in the male fertile line '2006H', was cloned, respectively. The three sequences correspond to the same gene with two alleles: Rfob in '9802H' and rfob in '9802A1' and '2006H'. These two alleles differ from Rfo/Rfk1 and rfk1 (AJ535624) alleles by two synonymous base substitutions, respectively. Based on the differences between the Rfob and rfob genes, one PCR-based marker was developed, and designated Marker 1, which is identical to the corresponding region of Rfob by sequence analysis. In the F(2) segregating population described above, the Marker 1 was present in 5 sterile plants and in 453 fertile plants, absent in 4 fertile plants and in 138 sterile plants, and was found to fit a segregation ratio 3:1 indicating that Rfob was single copy in '9802H'. Linkage analysis showed that the Rfo2 locus for our CMS-Rf system was distant from the Rfo locus by about 1.6 cM. The sterile line '9802A1' was pollinated by the male fertile line '2006H' and the resulting F(1) plants were all male fertile. These results indicated that the male fertility of radish CMS can be restored by a new Rf locus, which linked tightly to the Rfo locus.

Male Sterile Lines of Zinnia elegans and Their Cytological Observations

In order to find out a new pathway for utilizing heterosis of Zinnia elegans and accelerate breeding process, the mechanism of anther development of a male sterile line was explored. Backcross, sibmating, selfing of fertile plants and testcross with inbred lines were analyzed and identified in the field, and cytology was observed. Recessive nucleus male sterile line AH209AB capable of being a maintainer was obtained by successive backcrosses with male sterile plants and fertile F1 plants as male parents. Cytological and anatomical studies indicated that: (1) The wall of normal anther was constituted of four layers of cells such as epidermis, powder chamber wall, middle level and tapetum cells. The process in meiosis of pollen mother cell in Zinnia elegans was normal and cytoplasm divided simultanously. Mature pollen grain was tricellular type. (2) The petal of male sterile plant degraded as a thread-like structure, the stamens were villiform in appearance and no pollens were formed. The result showed that the anther of male sterile plant no longer proceed to differentiate spore mother cell and the pollen sac after the formation of the tissue of sporogenous cells, there was no evident boundary between tapetum cell, middle lamella and inner wall of PMC, tapetal cells did not develop from the very beginning. So the abortion type was completely structural male sterility. The male sterile line belongs to non-sporange male sterile type and is of great use in F1 seeds production.

Mitochondrial nad2 gene is co-transcripted with CMS-associated orfB gene in cytoplasmic male-sterile stem mustard (Brassica juncea)

The transcriptional patterns of mitochondrial respiratory related genes were investigated in cytoplasmic male-sterile and fertile maintainer lines of stem mustard, Brassica juncea. There were numerous differences in nad2 (subunit 2 of NADH dehydrogenase) between stem mustard CMS and its maintainer line. One novel open reading frame, hereafter named orfB gene, was located at the downstream of mitochondrial nad2 gene in the CMS. The novel orfB gene had high similarity with YMF19 family protein, orfB in Raphanus sativus, Helianthus annuus, Nicotiana tabacum and Beta vulgaris, orfB-CMS in Daucus carota, atp8 gene in Arabidopsis thaliana, 5' flanking of orf224 in B. napus (nap CMS) and 5' flanking of orf220 gene in CMS Brassica juncea. Three copies probed by specific fragment (amplified by primers of nad2F and nad2R from CMS) were found in the CMS line following Southern blotting digested with HindIII, but only a single copy in its maintainer line. Meanwhile, two transcripts were shown in the CMS line following Northern blotting while only one transcript was detected in the maintainer line, which were probed by specific fragment (amplified by primers of nad2F and nad2R from CMS). Meanwhile, the expression of nad2 gene was reduced in CMS bud compared to that in its maintainer line. We thus suggested that nad2 gene may be co-transcripted with CMS-associated orfB gene in the CMS. In addition, the specific fragment that was amplified by primers of nad2F and nad2R just spanned partial sequences of nad2 gene and orfB gene. Such alterations in the nad2 gene would impact the activity of NADH dehydrogenase, and subsequently signaling, inducing the expression of nuclear genes involved in male sterility in this type of cytoplasmic male sterility.

Progress in Research and Development on Hybrid Rice: A Super-domesticate in China

BackgroundChina has been successful in breeding hybrid rice strains, but is now facing challenges to develop new hybrids with high-yielding potential, better grain quality, and tolerance to biotic and abiotic stresses. This paper reviews the most significant advances in hybrid rice breeding in China, and presents a recent study on fine-mapping quantitative trait loci (QTLs) for yield traits.ScopeBy exploiting new types of male sterility, hybrid rice production in China has become more diversified. The use of inter-subspecies crosses has made an additional contribution to broadening the genetic diversity of hybrid rice and played an important role in the breeding of super rice hybrids in China. With the development and application of indica-inclined and japonica-inclined parental lines, new rice hybrids with super high-yielding potential have been developed and are being grown on a large scale. DNA markers for subspecies differentiation have been identified and applied, and marker-assisted selection performed for the development of restorer lines carrying disease resistance genes. The genetic basis of heterosis in highly heterotic hybrids has been studied, but data from these studies are insufficient to draw sound conclusions. In a QTL study using stepwise residual heterozygous lines, two linked intervals harbouring QTLs for yield traits were resolved, one of which was delimited to a 125-kb region.ConclusionsAdvances in rice genomic research have shed new light on the genetic study and germplasm utilization in rice. Molecular marker-assisted selection is a powerful tool to increase breeding efficiency, but much work remains to be done before this technique can be extended from major genes to QTLs.

Structural and Expressional Variations of the Mitochondrial Genome Conferring the Wild Abortive Type of Cytoplasmic Male Sterility in Rice

AbstractThe so‐called “wild abortive” (WA) type of cytoplasmic male sterility (CMS) derived from a wild rice species Oryza rufipogon has been extensively used for hybrid rice breeding. However, extensive analysis of the structure of the related mitochondrial genome has not been reported, and the CMS‐associated gene(s) remain unknown. In this study, we exploited a mitochondrial genome‐wide strategy to examine the structural and expressional variations in the mitochondrial genome conferring the CMS. The entire mitochondrial genomes of a CMS‐WA line and two normal fertile rice lines were amplified by Long‐polymerase chain reaction into tilling fragments of up to 15.2 kb. Restriction and DNA blotting analyses of these fragments revealed that structural variations occurred in several regions in the WA mitochondrial genome, as compared to those of the fertile lines. All of the amplified fragments covering the entire mitochondrial genome were used as RNA blot probes to examine the mitochondrial expression profile among the CMS‐WA and fertile lines. As a result, only two mRNAs were found to be differentially expressed between the CMS‐WA and the fertile lines, which were detected by a probe containing the nad5 and orf153 genes and the other having the ribosomal protein gene rpl5, respectively. These mRNAs are proposed to be the candidates for further identification and functional studies of the CMS gene.

Rice UDP-Glucose Pyrophosphorylase1 Is Essential for Pollen Callose Deposition and Its Cosuppression Results in a New Type of Thermosensitive Genic Male Sterility

UDP-glucose pyrophosphorylase (UGPase) catalyzes the reversible production of glucose-1-phosphate and UTP to UDP-glucose and pyrophosphate. The rice (Oryza sativa) genome contains two homologous UGPase genes, Ugp1 and Ugp2. We report a functional characterization of rice Ugp1, which is expressed throughout the plant, with highest expression in florets, especially in pollen during anther development. Ugp1 silencing by RNA interference or cosuppression results in male sterility. Expressing a double-stranded RNA interference construct in Ugp1-RI plants resulted in complete suppression of both Ugp1 and Ugp2, together with various pleiotropic developmental abnormalities, suggesting that UGPase plays critical roles in plant growth and development. More importantly, Ugp1-cosuppressing plants contained unprocessed intron-containing primary transcripts derived from transcription of the overexpression construct. These aberrant transcripts undergo temperature-sensitive splicing in florets, leading to a novel thermosensitive genic male sterility. Pollen mother cells (PMCs) of Ugp1-silenced plants appeared normal before meiosis, but during meiosis, normal callose deposition was disrupted. Consequently, the PMCs began to degenerate at the early meiosis stage, eventually resulting in complete pollen collapse. In addition, the degeneration of the tapetum and middle layer was inhibited. These results demonstrate that rice Ugp1 is required for callose deposition during PMC meiosis and bridges the apoplastic unloading pathway and pollen development.

A Honglian CMS line of rice displays aberrant F0 of F0F1-ATPase

Honglian (HL) is one of the three major types of cytoplasmic male sterility (CMS) of rice (Oryza sativa L) that has been commercially used in hybrid production. In previous studies, the CMS in HL is shown to be associated with a chimeric gene orfH79 that is cotranscribed with an extra atp6 in mitochondria. This study demonstrated that the intact F0F1-ATPase in HL CMS line was specifically reduced in both of its protein quantity and enzyme activity, whereas its F1 sector was not affected. It implies that the F0 sector presents a labile linkage with F1. In the presence of fertility restorer gene, F0F1-ATPase can be recovered. Furthermore, orfH79 transcripts were preferentially polyadenylated, and consequently degraded rapidly in florets of the restored hybrid plants, indicating that the atp6-orfH79 is involved in the sterile phenotype. With inhibition of cytochrome pathway of electron transfer chain, the biomass of the sterile plants grown in dark was significantly lower than that of the fertile lines. However, the respiration measurements showed an increase in the electron transferring capacity in the sterile plants, suggesting that the reduction of biomass in sterile line was caused by the disruption of F0F1-ATPase.

Cytological and molecular characterization of a novel monogenic dominant GMS in Brassica napus L.

A novel genic male sterile (GMS) line in Brassica napus L., which was identified in 1999, was found to be controlled by a monogenic dominant gene, which we have designated as MDGMS. The microspores of the MDGMS abort before the degradation of the tapetal cell layer. The F1 fertility from any fertile lines crossed with MDGMS segregated and the ratio was close to 1:1. Bulked segregation analysis (BSA) was employed to identify random amplified polymorphic DNA (RAPD) markers linked to the Ms gene in MDGMS. Among 880 random 10-mer oligonucleotide primers screened against the bulk DNA of sterile and fertile, one primer S243 (5'-CTATGCCGAC-3') gave a repeatable 1500-bp DNA polymorphic segment S243(1500) between the two bulks. Analysis of individual plants of each bulks and other types of GMS and cytoplasmic male sterility (CMS) lines suggest that the RAPD marker S243(1500) is closely linked to the MDGMS locus in rapeseed. This RAPD marker has been converted into sequence characterized amplified region (SCAR) marker to aid identification of male-fertility genotypes in segregating progenies of MDGMS in marker-assisted selection (MAS) breeding programs.

Penampilan Fenotipik dan Tingkat Kemandulan Tepungsari Calon Galur Mandul Jantan Tipe Wild Abortive

Wild Abortive (WA) type of cytoplasmic male sterility (CMS) was developed by Indonesian Center of Rice Research, Sukamandi through backcross method. Pollen sterility and phenotypic acceptability evaluation of cytoplasmic male sterile (CMS) candidates were considered important in CMS development process. Both of evaluation were done during dry season 2002 and wet season 2002/2003. The materials were 18 CMS candidates and their resembled maintainers. Each line planting on two rows (2.5 m each) with 20 x 20 cm spacing. Observations were done for 50% flowering time, pollen sterility and phenotypic acceptability. The results of observations showed that : (a) the variation of pollen sterility among 18 CMS candidates were 82.5 - 100%; (b) Nine CMS candidates were consistent in sterility (100%) and good in phenotypic acceptability during the two seasons. Those lines were derived from IR62829A/BP1082, IR68897A/S3613F, IR66707A/Barumun, IR58025A/S24731, IR62829A/BP68C, IR68886A/IR71605, IR66707A/A2790, IR69622A/IRBB5 and IR68886A/T12357. The male parent as donor were elite lines with some good characters such as good eating quality, resistant to Rice Tungro Virus (RTV) and Bacterial Leaf Blight (BLB). Key words : Rice, cytoplasmic male sterile, pollen sterility, phenotypic acceptability

Mechanism of cytoplasmic male-sterility modulated by mitochondrial retrograde regulation in higher plants

The type of cytoplasmic male-sterility, cytoplasmic male-sterility related mitochondrial factors, and nuclear restored gene-regulated mitochondrial factors in higher plants are reviewed in this paper. Based on gene regulation network for cytoplasmic male-sterility occurrence, we discussed and hypothesized that the interactions between nucleus and mitochondria determine cytoplasmic male-sterility occurrence modulated by mitochondrial retrograde regulation through possible mitochondrial retrograde signaling.

Damage of oxidative stress on mitochondria during microspores development in Honglian CMS line of rice

One of the cytoplasmic male sterility (CMS) types used for hybrid rice (Oryza sativa L.) production in China is the Honglian (HL)-CMS. Previous studies suggested that pollen abortion of the sterile plants was resulted from a special programmed cell death (PCD) program started at meiosis in the microspores. To elucidate the molecular basis of the pollen abortion, we compared the biochemical and physiological properties such as content of reactive oxygen species (ROS), ATP, NADH, total glutathione and ascorbate acid, the activities of dehydroascrbate reductase, glutathione reductase, ascorbate peroxides and superoxide dismutase, and the integrity of mitochondrial genome DNA isolated from an HL-CMS line, Yuetai A and its maintainer line, Yuetai B. Our results indicated that the mitochondria of the HL-CMS line suffered from a serious oxidative stress during microspores development. Oxidative stress induced by abnormal increased ROS at meiosis stage resulted in the depletion of ATP and NADH, and the degradation of mitochondrial genomic DNA. This suggests that the presence of redox signal originated in mitochondria affects the rest of the cell. Therefore, it is possible that the abortion of premature microspores in HL-CMS line is induced by the chronic oxidative stress in mitochondria in the early stage of pollen development.

Transcript profiling of a dominant male sterile mutant ( Ms-cd1) in cabbage during flower bud development

A spontaneous male-sterile mutation affecting anther development has been identified in cabbage line 79-399-3. The male sterility was associated with abnormal callose degeneration and failure of microspore separation during anther development. Three pairs near-isogenic lines (NILs) with or without the dominant male sterility allele ( MS-cd1) were profiled by cDNA-AFLP to detect differentially expressed genes during flower bud development. Out of 6500 transcript derived fragments (TDFs) inspected, 27 were differentially expressed between fertile and male sterile plants in all three sets of NILs. All 27 TDFs were sequenced and BLAST searching revealed that 14 out of 27 fragments were highly homologous to genes with known or predicted function in Arabidopsis. Moreover, three of these TDFs were homologous to genes involved in cell wall formation and degradation, including plant invertase/pectin methylesterase inhibitor (PMEI) and polysaccharide lyase. RT-PCR experiments revealed that PMEI was expressed strongly in the anther and filament. Analysis of a set of NILs with different male sterility types showed that PMEI was also not expressed in a Nigra CMS NIL, a recessive male sterile NIL and an Ogura CMS NIL compared to their corresponding fertile NILs. Based on both cytological and transcriptional data we suggest that the dominant MS-cd1 mutant gene may disrupts proper separation of pollens from tetrads, which leads to the suppressed expression of a number of genes including BoPMEI1, a gene likely involved in the degradation of pectin.

Biological effects of carbon-ion beam on induction of male-sterility and a novel season-dependent floral homeotic mutant in Solanum villosum Miller

SummaryThis study was conducted to determine the biological effects of a 12C5+ ion beam on male-sterility in Solanum villosum, a leafy vegetable whose consumption and demand continues to escalate due to its high nutritional and medicinal value. S. villosum is still underutilised due to low vegetative yields that have hampered full domestication and commercialisation. Yields are limited mainly by prolific early flowering and excess fruit and seed set in competition with leaf expansion and productivity. Thus, there is a need to reduce this overbearing in order to circumvent the source-sink imbalances that occur after anthesis. Carbon-ion beam-induced male-sterility is proposed as a possible strategy. Based on overall plant development from germination rate, seedling survival frequency, the proportion of self-fertile M1 plants, and the frequency of diverse growth and development mutants in the M2 progeny, with an emphasis on male-sterility, 20–30 Gy of 12C5+ ions was determined to be optimum. Four male-sterile mutant types (T-1, T-2, T-3, T-4) similar to those reported from a previous -ray mutation study were isolated at higher frequencies. In addition, a novel abnormal floral organ mutant (T-5), whose flowers were sepalloid in mid-Spring, stamen-less in late-Spring, indeterminate in Summer and whose structure and fertility was partially restored, with berry and seed set in Autumn, was isolated. This restoration is potentially useful for seed propagation since the self-fertile seed progeny of the T-5 mutant were 100% male-sterile (sepalloid). Maintenance by seed has been made possible by conditional partial restoration of fertility that occurs in a regular and stable pattern.

Male-sterility induced by gamma-ray irradiation of African nightshade (Solanum nigrum L. ssp. villosum) seed

SummaryThe leaf yields of vegetables belonging to the Solanum nigrum complex are limited by prolific early flowering and berry set. Source-sink limitations and imbalances occur after anthesis, with dry matter partitioning directed more to pollen, seed and fruit formation and development. Each of these processes is associated with high respiratory costs, in competition with leaf expansion and productivity. To use male-sterility to redistribute biological biomass towards greater economic leaf yield, a range of mutants inducible by irradiation of seed with gamma-rays was investigated. On the basis of overall plant development from germination, seedling survival, production of M2 selfed-seed and the frequency of male-sterile mutants, 100 Gy of gamma-rays was determined to be the optimum dose. Four male-sterile mutant types were isolated during the Spring-Summer season from the M2 screen: (i) an acetocarmine-stained non-viable pollen type which stained black with potassium iodide solution (T-1); (ii) a defective pollen type not stainable with acetocarmine (T-2); (iii) a pollen-less type with defective anthers (T-3); and (iv) an extremely low pollen-producing type (T-4). An intermediate type (T-1/2) had a mixture of acetocarmine stainable and defective non-stainable pollen. All T-1, and some T-3 mutants were partially restored and set berries with selfed-seed, while T-1/2 set non-seeded berries in the Autumn-Winter season. Eliminating the reproductive function and subsequently fruits, which are the major sink organs of the plant, is expected to enable the male-sterile mutants isolated in this study to use the biomass no longer allocated to pollen (and eventually to berry and seed production), for extra leaf production.

The cytoplasmic male-sterile type and normal type mitochondrial genomes of sugar beet share the same complement of genes of known function but differ in the content of expressed ORFs.

The complete nucleotide sequence (501,020 bp) of the mitochondrial genome from cytoplasmic male-sterile (CMS) sugar beet was determined. This enabled us to compare the sequence with that previously published for the mitochondrial genome of normal, male-fertile sugar beet. The comparison revealed that the two genomes have the same complement of genes of known function. The rRNA and tRNA genes encoded in the CMS mitochondrial genome share 100% sequence identity with their respective counterparts in the normal genome. We found a total of 24 single nucleotide substitutions in 11 protein genes encoded by the CMS mitochondrial genome. However, none of these seems to be responsible for male sterility. In addition, several other ORFs were found to be actively transcribed in sugar beet mitochondria. Among these, Norf246 was observed to be present in the normal mitochondrial genome but absent from the CMS genome. However, it seems unlikely that the loss of Norf246 is causally related to the expression of CMS, because previous studies on mitochondrial translation products failed to detect the product of this ORF. Conversely, the CMS genome contains four transcribed ORFs (Satp6presequence, Scox2-2 , Sorf324 and Sorf119) which are missing from the normal genome. These ORFs, which are potential candidates for CMS genes, were shown to be generated by mitochondrial genome rearrangements.