Final Report Summary - SWCD (Development of super-wheat crops by introgressing agronomic traits from related wild species)
Plant breeders play a major role in worldwide efforts to unzip gene functions and interactions, so increasing quality and productivity can only be achieved through “science-based” rather than “traditional” agriculture. Wheat is one of the most important food crops in the world and breeders have been using related species as genetic donors with the aim of widen the genetic basis of this crop to get, for example, wheat cultivars better adapted to specific agro-climatic conditions, carrying resistance to pests, etc. Despite its genome complexity, wheat behaves as diploid during meiosis, the cellular process for producing gametes in sexually reproducing organisms. This means that each chromosome only associate with its identical (homologous) and not with related chromosomes. The major locus stabilising chromosome pairing during meiosis is the Ph1 locus. In contrast, such stable chromosome associations are preventing pairing between wheat chromosomes and those from other species carrying desirable agronomic traits; therefore the Ph1 locus has a negative effect for plant breeding purposes. Understanding the biology of this phenotype to switch it temporary off will contribute to complete the breeding goals of this proposal.
The project was focused in two goals: 1) to deepen our knowledge on chromosome pairing during meiosis in wheat and an applied one, 2) to transfer into wheat desirable agronomic traits from related wild species such as Hordeum chilense, a wild barley carrying genes, among others, codifying for high carotene content on chromosome 7Hch or resistance to Septoria tritice on chromosome 4Hch. This breeding goal can be approached by promoting inter-specific recombination between wheat chromosomes and those from H. chilense in the background of the ph1 mutant.
Replication was studied during premeiosis and early meiosis in wheat using flow cytometry, which has allowed the quantification of the amount of DNA in wheat anther in each phase of the cell cycle during premeiosis and each stage of early meiosis. Flow cytometry has been revealed as a suitable and user-friendly tool to detect and quantify DNA replication during early meiosis in wheat. Chromosome replication was detected in wheat during premeiosis and early meiosis until pachytene, when chromosomes associate in pairs. We showed that the Ph1 locus plays an important role on the length of meiotic DNA replication in wheat, particularly affecting the rate of replication during early meiosis in wheat. Moreover, the observation of homologue pairing between a pair of H. chilense chromosomes lacking the subtelomeric region on one chromosome arm indicated that the subtelomeric region is important for the process of homologous chromosome recognition and pairing.
On the breeding side, the ph1b mutant has been exploited to induced allosyndesis between wheat chromosomes and those of H. chilense. A number of single chromosome H. chilense substitution and addition lines in wheat were crossed and backcrossed to the ph1b mutant to produce plants in which pairing between the wheat and the non-wheat chromosomes was not suppressed by the presence of Ph1. Genomic in situ hybridization was applied to almost 500 BC1F2 progeny as a screen for allosyndetic recombinants. Chromosome rearrangements were detected affecting H. chilense chromosomes 4Hch, 5Hch, 6Hch and 7Hch. Among these, it is worth to say that durum wheat lines carrying either a full chromosome 4Hch or chromosome arms 4HchS or 4HchL (short or long arm, respectively) from H. chilense with genes conferring resistance to Septoria tritice were obtained. Simultaneously, crosses between the 7Hch H. chilense substitution lines in wheat and the ph1 mutant allowed the development of wheat-H. chilense translocation lines for both 7 HchS and 7 HchL chromosome arms in the wheat background. The carotenoid content in 7HchS-7AL and 7AS-7 HchL disomic translocation lines was higher than the wheat-7Hch addition line and double amount of carotenoids than the wheat itself. The Psy1 (Phytoene Synthase1) gene, which is the first committed step in the carotenoid biosynthetic pathway, was also cytogenetically mapped on the 7HchS chromosome arm. These new wheat-H. chilense translocation lines can be used as a powerful tool in wheat breeding programs to enrich the diet in bioactive compounds.
The project was focused in two goals: 1) to deepen our knowledge on chromosome pairing during meiosis in wheat and an applied one, 2) to transfer into wheat desirable agronomic traits from related wild species such as Hordeum chilense, a wild barley carrying genes, among others, codifying for high carotene content on chromosome 7Hch or resistance to Septoria tritice on chromosome 4Hch. This breeding goal can be approached by promoting inter-specific recombination between wheat chromosomes and those from H. chilense in the background of the ph1 mutant.
Replication was studied during premeiosis and early meiosis in wheat using flow cytometry, which has allowed the quantification of the amount of DNA in wheat anther in each phase of the cell cycle during premeiosis and each stage of early meiosis. Flow cytometry has been revealed as a suitable and user-friendly tool to detect and quantify DNA replication during early meiosis in wheat. Chromosome replication was detected in wheat during premeiosis and early meiosis until pachytene, when chromosomes associate in pairs. We showed that the Ph1 locus plays an important role on the length of meiotic DNA replication in wheat, particularly affecting the rate of replication during early meiosis in wheat. Moreover, the observation of homologue pairing between a pair of H. chilense chromosomes lacking the subtelomeric region on one chromosome arm indicated that the subtelomeric region is important for the process of homologous chromosome recognition and pairing.
On the breeding side, the ph1b mutant has been exploited to induced allosyndesis between wheat chromosomes and those of H. chilense. A number of single chromosome H. chilense substitution and addition lines in wheat were crossed and backcrossed to the ph1b mutant to produce plants in which pairing between the wheat and the non-wheat chromosomes was not suppressed by the presence of Ph1. Genomic in situ hybridization was applied to almost 500 BC1F2 progeny as a screen for allosyndetic recombinants. Chromosome rearrangements were detected affecting H. chilense chromosomes 4Hch, 5Hch, 6Hch and 7Hch. Among these, it is worth to say that durum wheat lines carrying either a full chromosome 4Hch or chromosome arms 4HchS or 4HchL (short or long arm, respectively) from H. chilense with genes conferring resistance to Septoria tritice were obtained. Simultaneously, crosses between the 7Hch H. chilense substitution lines in wheat and the ph1 mutant allowed the development of wheat-H. chilense translocation lines for both 7 HchS and 7 HchL chromosome arms in the wheat background. The carotenoid content in 7HchS-7AL and 7AS-7 HchL disomic translocation lines was higher than the wheat-7Hch addition line and double amount of carotenoids than the wheat itself. The Psy1 (Phytoene Synthase1) gene, which is the first committed step in the carotenoid biosynthetic pathway, was also cytogenetically mapped on the 7HchS chromosome arm. These new wheat-H. chilense translocation lines can be used as a powerful tool in wheat breeding programs to enrich the diet in bioactive compounds.