Method for the mapping of a female partial-sterile locus on a molecular marker linkage map

Characterization and fine mapping of a female fertility associated gene Ff1(t) in rice

Female-sterile line can be used as a pollinator which has a great potential for hybrid seeds production. However, reports on female fertility are fewer than male fertility. Here, we characterized a recessive female fertility weakening mutant ff1(t) from rice. The spikelet fertility was seriously affected in the mutant. Reciprocal crosses and pollen vitality assay suggest that the decreased fertility was caused by the defective female gametophytes. Further investigation indicated that the mutant ovary development was inhibited before fertilization and failed swelling after flowering. Genetic analysis and fine mapping showed that the mutant was controlled by a single recessive gene, residing on a 16.8 kb region on the long arm of chromosome 1. The gene annotation indicated that there was only one putative gene encoding lysine decarboxylase-like protein in this region, which was allelic to LOG. Further, the sequence analysis was carried out and a substitution at the splice site of intron 2 / exon 3 was revealed in ff1(t) mutant, resulting in the change of reading frame. The finding of novel allele of LOG locus will facilitate the understanding of the mechanisms of female gametophyte development.

Genetic mapping of sterile genes with epistasis in backcross designs

The mapping of sterile genes is an essential issue, which should be solved for the investigation of sterility mechanism in wide hybridization of plants. However, the methods formerly developed cannot address the problem of mapping sterile loci with epistasis. In this study, we developed a new method to map sterile genes with epistasis in wide hybridizations of plants using a backcross design. The maximum likelihood method was used to estimate the parameters of recombination fractions and effects of sterile genes, and the convergent results of these parameters were obtained using the expectation maximization (EM) algorithm. The application and efficiency of this method were tested and demonstrated by a set of simulated data and real data analysis. Results from the simulation experiments showed that the method works well for simultaneously estimating the positions and effects of sterile genes, as well as the epistasis between sterile genes. A real data set of a backcross (BC) population from an interspecific hybrid between cultivated rice, Oryza sativa, and its wild African relative, Oryza longistaminata, was analyzed using the new method. Five sterile genes were detected on the chromosomes of 1, 3, 6, 8 and 10, and significant epistatic effects were found among the four pairs of sterile genes.

Phenotypic characterization and genetic analysis of a partially female-sterile mutant in Brassica napus

mfs is a partially female-sterile Brassica napus mutant derived from a spontaneous mutation. When the mutant is crossed as a female, very poor seed set is obtained, whereas it is fertile as a pollen donor. The floret of the mutant consisted of almost equal-length stamens, a short pistil, a flat style and ovary, and the stigma was chapped. Measures of pollen viability and pollen tube growth in vitro indicated that the mutation enhanced pollen viability. The papillae of mfs consisted of two conjoint bilobed domes, and the papillar cells were sparse, oblate and large at anthesis, but become withered and senesced quickly afterward. Pollen grains could germinate over the papillar cells, but pollen tubes could not penetrate into it. After flower opening, the number of organelles in mfs papillar cell decreased, the structure of it distinctly degenerated, and vacuolization was abnormally high. Genetic analysis of 3 F2 populations and 3 BC1F1 populations suggested that the mutant trait was controlled by two recessive genes.

Detection of segregation distortion loci in triticale (x Triticosecale Wittmack) based on a high-density DArT marker consensus genetic linkage map

Background

Triticale is adapted to a wide range of abiotic stress conditions, is an important high-quality feed stock and produces similar grain yield but more biomass compared to other crops. Modern genomic approaches aimed at enhancing breeding progress in cereals require high-quality genetic linkage maps. Consensus maps are genetic maps that are created by a joint analysis of the data from several segregating populations and different approaches are available for their construction. The phenomenon that alleles at a locus deviate from the Mendelian expectation has been defined as segregation distortion. The study of segregation distortion is of particular interest in doubled haploid (DH) populations due to the selection pressure exerted on the plants during the process of their establishment.

Results

The final consensus map, constructed out of six segregating populations derived from nine parental lines, incorporated 2555 DArT markers mapped to 2602 loci (1929 unique). The map spanned 2309.9 cM with an average number of 123.9 loci per chromosome and an average marker density of one unique locus every 1.2 cM. The R genome showed the highest marker coverage followed by the B genome and the A genome. In general, locus order was well maintained between the consensus linkage map and the component maps. However, we observed several groups of loci for which the colinearity was slightly uneven. Among the 2602 loci mapped on the consensus map, 886 showed distorted segregation in at least one of the individual mapping populations. In several DH populations derived by androgenesis, we found chromosomes (2B, 3B, 1R, 2R, 4R and 7R) containing regions where markers exhibited a distorted segregation pattern. In addition, we observed evidence for segregation distortion between pairs of loci caused either by a predominance of parental or recombinant genotypes.

Conclusions

We have constructed a reliable, high-density DArT marker consensus genetic linkage map as a basis for genomic approaches in triticale research and breeding, for example for multiple-line cross QTL mapping experiments. The results of our study exemplify the tremendous impact of different DH production techniques on allele frequencies and segregation distortion covering whole chromosomes.

Further mapping of quantitative trait loci for female sterility in wheat (Triticum aestivum L.)

Epistasis underlying fertility plays an important role in crop breeding. Although a new female sterile mutant in wheat, XND126, has been identified and a major quantitative trait locus (QTL), taf1, for the female sterility has been mapped, the genetic architecture of the female sterility needs to be further addressed. To identify the interaction involving the gene(s) controlling the female sterility, an investigation was carried out for the seed setting ratio in an F2 population derived from the cross between XND126 and Gaocheng 8901. Among 1250 simple sequence repeat (SSR) primer pairs in the whole genome, a total of 21 markers, obtained by recessive class approach, along with other ten tightly linked markers on reference maps in wheat, were used to survey 243 F2 individuals. As a result, 28 markers were mapped into five genetic linkage groups. The performance for female sterility for each F2 individual was evaluated simultaneously at the Urumqi and Huai'an experimental stations in 2006-2007. The two phenotypic datasets along with marker information were jointly analysed in the detection of QTL using penalized maximum likelihood approach. A total of six QTLs, including two main-effect QTLs, three epistatic QTLs and one environmental interaction and accounting for 0.67-24.55% of the total phenotypic variance, were identified. All estimated effects accounted for 53.26% of the total phenotypic variation. The taf1 detected in previous study was also located on the same marker interval on chromosome 2DS. These results enrich our understanding of the genetic basis of the female sterility.