Homoeologous Recombination-Based Chromosome Engineering for Physical Mapping and Introgression in Wheat and Its Relatives Aegilops speltoides and Thinopyrum elongatum
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Homoeologous Recombination-Based Chromosome Engineering for Physical Mapping and Introgression in Wheat and Its Relatives Aegilops speltoides and Thinopyrum elongatum (2.346Mb)
Wheat (genome AABBDD) is one of the essential crops, offering approximate 20% of human calorie consumption worldwide. Allopolyploidization of three diploid ancestors led to hexaploid wheat with narrowed genetic variation. Chromosome engineering is an applicable approach to restore the evolutionarily-omitted genetic diversity by homoeologous chromosomes recombination between wheat and its relatives. Two diploid relatives of wheat, Thinopyrum elongatum (genome EE) and Aegilops speltoides (genome SS), containing favorable genes, are used as gene resources for alien introgression and genome diversification in wheat. An advanced and effective experiment procedure was developed and applied for the production, recovery, detection, and characterization of homoeologous recombinants. Meanwhile, a novel recombinant chromosome recovery strategy was exploited with improved efficiency and accuracy. In this study, recombinants of wheat chromosomes 3B and 7B with their homoeologous chromosomes in Th. elongatum and Ae. speltoides (i.e. 3B-3E, 7B-7E, and 7B-7S) were produced and detected. Totolly, 81 3B-3E recombinants and four aberrations involving in distinct chromosomal regions were developed in three recombination cycles by fluorescent genomic in situ hybridization (FGISH). The secondary and tertiary recombination breakpoints occurred toward the proximal regions comparing to the primary recombination under this advanced recombination procedure. A novel recovery strategy was used to recover 7B-7E and 7B-7S homoeologous recombinants by chromosome-specific markers and FGISH verification. Marker-based pre-screening and subsequent FGISH verification identified 29 7B-7E and 61 7B- 7S recombinants, seven 7B-7E and four 7B-7S Robertsonian translocations, one 7E and five 7S telocentric chromosomes, and three 7S deletions. All the recombinants and aberrations were genotyped by high-throughput wheat 90K single nucleotide polymorphism (SNP) assay and the recombination breakpoints were physically mapped to wheat chromosome 3B or 7B according to their FGISH patterns, SNP results, and wheat reference genome sequence. Chromosome 3B was physically partitioned into 38 bins with 429 SNPs. Meanwhile, 44 distinct bins were resolved for chromosome 7B with 523 SNPs. A composite bin map was constructed for chromosomes 3B and 7B, respectively, with a comprehensive analysis of FGISH and SNPs results. In summary, this project provides a unique physical framework for further wheat genome studies and diversifies the wheat genome for germplasm development in wheat breeding.