Dynamics of DNA replication during premeiosis and early meiosis in wheat

Meiosis is a specialised cell division that involves chromosome replication, two rounds of chromosome segregation and results in the formation of the gametes. Meiotic DNA replication generally precedes chromosome pairing, recombination and synapsis in sexually developing eukaryotes. In this work, replication has been 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 the stage of pachytene, when chromosomes are associated in pairs to further recombine and correctly segregate in the gametes. In addition, the effect of the Ph1 locus, which controls chromosome pairing and affects replication in wheat, was also studied by flow cytometry. Here 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.This research was supported by grant ERC-StG- 243118 from the FP7 and The European Regional Development Fund (FEDER) from the European Union.Peer Reviewe

The subtelomeric region is important for chromosome recognition and pairing during meiosis

The process of meiosis results in the formation of haploid daughter cells, each of which inherit a half of the diploid parental cells' genetic material. The ordered association of homologues (identical chromosomes) is a critical prerequisite for a successful outcome of meiosis. Homologue recognition and pairing are initiated at the chromosome ends, which comprise the telomere dominated by generic repetitive sequences, and the adjacent subtelomeric region, which harbours chromosome-specific sequences. In many organisms telomeres are responsible for bringing the ends of the chromosomes close together during early meiosis, but little is known regarding the role of the subtelomeric region sequence during meiosis. Here, the observation of homologue pairing between a pair of Hordeum chilense chromosomes lacking the subtelomeric region on one chromosome arm indicates that the subtelomeric region is important for the process of homologous chromosome recognition and pairing.This research was supported by ERC-Starting Grant-243118 from the FP7 and The European Regional Development Fund (ERDF) from the European Union and by the AGL2012-33264 from the Spanish Economy and Competitiveness Ministry.Peer Reviewe

Novel Bread Wheat Lines Enriched in Carotenoids Carrying Hordeum chilense Chromosome Arms in the ph1b Background

The use of crop wild relative species to improve major crops performance is well established. Hordeum chilense has a high potential as a genetic donor to increase the carotenoid content of wheat. Crosses between the 7Hch H. chilense substitution lines in wheat and the wheat pairing homoeologous1b (ph1b) mutant allowed the development of wheat-H. chilense translocation lines for both 7Hchα and 7Hchβ chromosome arms in the wheat background. These translocation lines were characterized by in situ hybridization and using molecular markers. In addition, reverse phase chromatography (HPLC) analysis was carried out to evaluate the carotenoid content and both 7Hchα∙7AL and 7AS∙7Hchβ disomic translocation lines. The carotenoid content in 7Hchα∙7AL and 7AS∙7Hchβ disomic translocation lines was higher than the wheat-7Hch addition line and double amount of carotenoids than the wheat itself. A proteomic analysis confirmed that the presence of chromosome 7Hch introgressions in wheat scarcely altered the proteomic profile of the wheat flour. The Psy1 (Phytoene Synthase1) gene, which is the first committed step in the carotenoid biosynthetic pathway, was also cytogenetically mapped on the 7Hchα 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.This work was supported by the ERC Starting Grant 243118 (http://www.ias.csic.es/ercstg-superwheatcrops/).Peer reviewe

The use of the ph1b mutant to induce recombination between the chromosomes of wheat and barley

Intensive breeding has led to a narrowing in the genetic base of our major crops. In wheat, access to the extensive gene pool residing in its many and varied relatives (some cultivated, others wild) is hampered by the block on recombination imposed by the Ph1 (Pairing homoeologous 1) gene. Here, the ph1b mutant has been exploited to induced allosyndesis between wheat chromosomes and those of both Hordeum vulgare (cultivated barley) and H. chilense (a wild barley). A number of single chromosome Hordeum sp. 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 and H. vulgare chromosomes 4Hv, 6Hv, and 7Hv. Two of these were clearly the product of a recombination event involving chromosome 4Hch and a wheat chromosome.This research was supported by grant ERC-StG-243118 awarded by the European Union under FP7 and The European Regional Development Fund (FEDER).Peer reviewedPeer Reviewe

Chromosome pairing between Hordeum and wheat can be promoted in the absence of the Ph1 locus

Póster presentado en Plant and Animal Genome XXI, celebrada en San Diego del 12 al 16 de enero de 2013.Wheat is an allopolyploid which has two or more sets of related chromosomes as the result of doubling chromosomes following sexual hybridization between closely related species. Hexaploid (bread) wheat contains A, B and D genomes and tetraploid (pasta) wheat contains A and B genomes. Despite their genome complexity, wheat behave as iploids during meiosis (each chromosome only pairs with its identical, homologue, and not with related or homoelogous chromosomes). Chromosome pairing is controlled in wheat by the Ph1 locus, which suppresses homoeologous chromosome pairing. Therefore the hybridization be tween polyploid wheat and related species caused inter-specific hybrids without chromosome pairing between wheat and related species. However, in the absence of the Ph1 locus (ph1 mutant) the chance of pairing between related chromosomes is increased. In this work, we exploit the ph1 mutant to development new wheat germplas m carrying introgressions from Hordeum chilense, a wild barley with high potential for wheat breed ing due to its agronomical traits such as resistance to some diseases or high antioxidant content. In the absence of the Ph1 locus chromosome specificity has been suppressed in this project, allowing inter-specific chromosome associations between wheat and H. chilense for the first time. Chromosome pairing and recombination between H. chilense and wheat chromosomes were detected by genomic in situ hybridization. A summary of the breeding program carried out to transfer desirable agronomic traits from H. chilense into wheat is reviewed in this work.This research was supported by ERC-Starting Grant-243118 from the FP7 and The European Regional Development Fund (FEDER) from the European Union.Peer Reviewe

Bread wheat breeding in the background of the ph1 mutants to transfer agronomic desirable traits from Hordeum chilense into wheat

Póster presentado en el 12th International Wheat Genetics Symposium, celebrado en Pacifico Yokohama (Japón) del 8 al 14 de septiembre de 2013.Cereals are a basic food for human population and are included in the Poaceace Family where the Triticeae tribe is. Wheat is one of the most important food crops in the wolrd, and understanding its genetics and genome organisation is of great value for genetics and plant breeding purposes.Peer Reviewe

Uses of the ph1 mutants as a genetic tool for wheat breeding

Ponencia presentada en el 7th International Triticeae Symposium celebrado en Chengdu Sichuan (China) del 9 al 13 de junio de 2013.The introgression of generic material from wild relatives into wheat germplasm is a classical and effective approach for broadening the genetic basis of this crop. Wheat is an allopolyploid which has two or more sets of related chromosomes (A, B and F genomes) as the result of doubling chromosomes following sexual hybridization between closely related species. Despite their genome complexity, wheat behaves as diploids durin meiosis (each chromosome only pairs with its identical, homologue, and not with related or homeoelogous chromosomes). Therefore the hybridization between polyploid or low level of pairing and recombination between wheat chromosomes and those from the wild relative species. The mayor factor preventing pairing between wheat and wild species chromosomes is the Ph1 locus.Peer Reviewe

Wheat, Rye, and Barley Genomes Can Associate during Meiosis in Newly Synthesized Trigeneric Hybrids

Polyploidization, or whole genome duplication (WGD), has an important role in evolution and speciation. One of the biggest challenges faced by a new polyploid is meiosis, in particular, discriminating between multiple related chromosomes so that only homologs recombine to ensure regular chromosome segregation and fertility. Here, we report the production of two new hybrids formed by the genomes of species from three different genera: a hybrid between Aegilops tauschii (DD), Hordeum chilense (HchHch), and Secale cereale (RR) with the haploid genomic constitution HchDR (n = 7× = 21); and a hybrid between Triticum turgidum spp. durum (AABB), H. chilense, and S. cereale with the constitution ABHchR (n = 7× = 28). We used genomic in situ hybridization and immunolocalization of key meiotic proteins to establish the chromosome composition of the new hybrids and to study their meiotic behavior. Interestingly, there were multiple chromosome associations at metaphase I in both hybrids. A high level of crossover (CO) formation was observed in HchDR, which shows the possibility of meiotic recombination between the different genomes. We succeeded in the duplication of the ABHchR genome, and several amphiploids, AABBHchHchRR, were obtained and characterized. These results indicate that recombination between the genera of three economically important crops is possible.This research was funded by the UK Biotechnology and Biological Research Council (BBSRC) through a grant of the Designing Future Wheat (DFW) Institute Strategic Programme (BB/P016855/1) and by the Spanish Ministry of Science, Innovation and Universities through the project PRIMA PCI2020-112027. M.-D.R. is grateful for the Juan de la Cierva-Incorporación contract IJC2018-035272-I from the Spanish Ministry of Science, Innovation and Universities.Peer reviewe

Pseudomonas fluorescens PICF7 displays an endophytic lifestyle in cultivated cereals and enhances yield in barley

Pseudomonas fluorescens PICF7, an indigenous inhabitant of olive roots, displays an endophytic lifestyle in this woody crop and exerts biocontrol against the fungal phytopathogen Verticillium dahliae. Here we report microscopy evidence that the strain PICF7 is also able to colonize and persist on or in wheat and barley root tissues. Root colonization of both cereal species followed a similar pattern to that previously reported in olive, including inner colonization of the root hairs. This demonstrates that strain PICF7 can colonize root systems of distant botanical species. Barley plants germinated from PICF7-treated seeds showed enhanced vegetative growth. Moreover, significant increases in the number of grains (up to 19.5%) and grain weight (up to 20.5%) per plant were scored in this species. In contrast, growth and yield were not significantly affected in wheat plants by the presence of PICF7. Proteomics analysis of the root systems revealed that different proteins were exclusively found depending on the presence or absence of PICF7 and only one protein with hydrogen ion transmembrane transporter activity was exclusively found in both PICF7-inoculated barley and wheat plants but not in the controls.This work was supported by grants from and (Convocatoria Proyectos de Excelencia from Junta de Andalucía, Spain), both co-funded by from the European Union (UE).Peer reviewe