The genetic basis of cytoplasmic male sterility and fertility restoration in wheat

Hybrid wheat varieties give higher yields than conventional lines but are difficult to produce due to a lack of effective control of male fertility in breeding lines. One promising system involves the Rf1 and Rf3 genes that restore fertility of wheat plants carrying Triticum timopheevii-type cytoplasmic male sterility (T-CMS). Here, by genetic mapping and comparative sequence analyses, we identify Rf1 and Rf3 candidates that can restore normal pollen production in transgenic wheat plants carrying T-CMS. We show that Rf1 and Rf3 bind to the mitochondrial orf279 transcript and induce cleavage, preventing expression of the CMS trait. The identification of restorer genes in wheat is an important step towards the development of hybrid wheat varieties based on a CMS-Rf system. The characterisation of their mode of action brings insights into the molecular basis of CMS and fertility restoration in plants.

Marker-assisted identification of potential fertility restorers for the development of three-line hybrids in rice (Oryza sativa L.)

Rice being a staple food crop of Kashmir valley, the focus is on enhancement of yield in order to meet the needs of ever-growing population.Identification of new parental lines is crucial for developing ecology-specific hybrids with ideal agronomic performance. Exploitation of heterosis in the form of hybrid rice technology can be one of the approaches to increase productivity in this crop, especially exploiting diversity among japonica lines can serve as an excellent route.A number of CMS lines suitable formountainous areas of Kashmir have been developed, however, the availability of promising restorer lines remains to be the major limitation for utilization of these lines.Identification of potential restorers acts as the main limiting factor for hybrid development in the Kashmir valley. Marker based screening for Rf3 and Rf4 fertility restorer genes can be helpful in rapid selection of restorer lines while dealing with the large quantity of genetic materials. In the present study, 100 rice germplasm were screened with the help of SSR markers, RM3148 and RM6100linked to Rf3 and Rf4 genes on chromosome 1 and 10, respectively. In total, 19 lines revealed the presence of both Rf3 and Rf4 genes. These lines amplified fertility restorer specific alleles for both the genes and may serve as potential restorers for obtaining heterotic rice hybrids. Further the germplasm lines were also evaluated for yield and quality traits.The present results would help in selection of suitable restorers along with preferred grain shape/size.

A multiplex PCR system for testing the genetic purity of hybrid rice (Oryza sativa L.)

Commercial exploitation of rice hybrid for sustainable production and productivity largely depends on genetic purity of hybrid seed used. To detect genetic impurity in the hybrid seeds developed through the three-line system using wild abortive (WA) cytoplasmic-based male sterility, a multiplex PCR assay was designed . A total of six primers, namely, DRRM-Rf3-10, Rf4-STS, RM6100, CMS-WA, osWA352 and RMS-3-WA352 were designed based on fertility restorer genes Rf3, Rf4 and Wa352. The primer combinations having RF4-STS and CMS-WA markers of Rf4 and WA352 genes, respectively showed clear and distinct PCR banding patterns among the WA-cytoplasm possessing 31A, fertile restorer PK117 lines and their cognate hybrid rice, Ajay. This multiplex PCR will be useful for assessment of genetic purity of hybrid rice seeds.

Identification of Suitable Restorers for WA-CMS Lines of Rice (Oryza sativa L.) through Conventional and Molecular Breeding Methods

The current study extensively evaluates 51 genotypes for their fertility restoration potential using test crosses with five WA (wild abortive) Cytoplasmic Male Sterile lines namely IR58025A, IR6897A, IR79156A, IR80559A and APMS6A. Also the genotypes were screened using SSR markers RM6100 and RM10313, tightly linked with the fertility restorer genes Rf4 and Rf3 respectively. The two way approach helped in identifying potential restorers for five WA-CMS lines and also detected the presence of dominant Rf genes in their genetic background. The R-lines identified can be safely presumed to be strong restorers for consecutive A-lines they were crossed with. The study also identified a potential maintainer CN1039-9 for the A-line IR58025A. The maintainer line identified can be later exploited for developing new CMS lines.

Genetic Resources for Fertility Restoration Lines and Maintainers of Capsicum annuum L.

Male fertility reactions of one hundred and forty-one accessions of chilies were classified. Three groups were found. Some accessions maintained male sterility and were determined to carry a non-sterile cytoplasm and to lack fertility restoration genes or N rfrf genotype. Some accessions segregated for the ability to restore male sterile cytoplasm and were determined to be heterozygous in restorer genes with genotype N/SRfrf. Some accessions restored fertility of CMS and had the genotype N/SRfRf. A few maintainers with good horticultural characteristics were selected. They were selfed and selected for a few generations and then their progeny were evaluated. There were differences in the genetic stability of cytoplasmic male-sterility among the selected lines. Some lines were good maintainers, but a few lines were discarded. The stable maintainers were distributed to 10 seed companies and the government of China. Some F1 hybrid chilies produced using these lines have been commercially sold both in China and Thailand. Fruit physio-chemical qualities of maintainer accessions, restorers and heterozygous accessions were also recorded. The level of capsaicin of the accessions varied from 3,250 to 8,850 Scoville units. The level of vitamin C showed a range of 4.43 to 103.16 mg./100g.fw. Horticultural characteristics of the accessions were recorded and the fruit physio-chemical qualities of the accessions were reported.

Homologous recombination changes the context of Cytochrome b transcription in the mitochondrial genome of Silene vulgaris KRA

BackgroundSilene vulgaris (bladder campion) is a gynodioecious species existing as two genders – male-sterile females and hermaphrodites. Cytoplasmic male sterility (CMS) is generally encoded by mitochondrial genes, which interact with nuclear fertility restorer genes. Mitochondrial genomes of this species vary in DNA sequence, gene order and gene content. Multiple CMS genes are expected to exist in S. vulgaris, but little is known about their molecular identity.ResultsWe assembled the complete mitochondrial genome from the haplotype KRA of S. vulgaris. It consists of five chromosomes, two of which recombine with each other. Two small non-recombining chromosomes exist in linear, supercoiled and relaxed circle forms. We compared the mitochondrial transcriptomes from females and hermaphrodites and confirmed the differentially expressed chimeric gene bobt as the strongest CMS candidate gene in S. vulgaris KRA. The chimeric gene bobt is co-transcribed with the Cytochrome b (cob) gene in some genomic configurations. The co-transcription of a CMS factor with an essential gene may constrain transcription inhibition as a mechanism for fertility restoration because of the need to maintain appropriate production of the necessary protein. Homologous recombination places the gene cob outside the control of bobt, which allows for the suppression the CMS gene by the fertility restorer genes. In addition, by analyzing RNA editing, we found the loss of three editing sites in the KRA mitochondrial genome and identified four sites with highly distinct editing rates between KRA and another S. vulgaris haplotypes (KOV). Three of these highly differentially edited sites were located in the transport membrane protein B (mttB) gene. They resulted in differences in MttB protein sequences between haplotypes despite completely identical gene sequences.ConclusionsFrequent homologous recombination events that are widespread in plant mitochondrial genomes may change chromosomal configurations and also the control of gene transcription including CMS gene expression. Posttranscriptional processes, e.g RNA editing shall be evaluated in evolutionary and co-evolutionary studies of mitochondrial genes, because they may change protein composition despite the sequence identity of the respective genes. The investigation of natural populations of wild species such as S. vulgaris are necessary to reveal important aspects of CMS missed in domesticated crops, the traditional focus of the CMS studies.