Introgression of chromosome 6PL terminal segment from Agropyron cristatum to increase both grain number and grain weight in wheat

Agropyron cristatum(2n=4x=28,PPPP),which harbours many high-yield and disease-resistance genes,is a promising donor for wheat improvement.Narrow genetic diversity and the trade-off between grain weight and grain number have become bottlenecks for increasing grain yield in wheat.In this study,a novel translocation line,WAT650l,was derived from the chromosome 6P addition line 4844–12,which can simultaneously increase both grain number per spike(GNS)and thousand-grain weight(TGW).Cytological analysis and molecular marker analysis revealed that WAT650l was a 5BL.5BS-6PL(bin 12–17)translocation line.Assessment of agronomic traits and analysis of the BC4F2 and BC5F2 populations suggested that the 6PL terminal chromosome segment in WAT650l resulted in increased grain number per spike(average increased by 14.07 grains),thousand-grain weight(average increased by 4.31 g),flag leaf length,plant height,spikelet number per spike and kernel number per spikelet during the two growing seasons of 2020–2021 and 2021–2022.Additionally,the increased GNS locus and high-TGW locus of WAT650l were mapped to the bins 16–17 and 12–13,respectively,on chromosome 6PL by genetic population analysis of three translocation lines.In summary,we provide a valuable germplasm resource for broadening the genetic base of wheat and overcoming the negative relationship between GNS and TGW in wheat breeding.

Chromosome 5P of Agropyron cristatum induces chromosomal translocation by disturbing homologous chromosome pairing in a common wheat background

Wide hybridization is a strategy for broadening the genetic basis of wheat. Because an efficient method for inducing wheat–alien chromosome translocations will allow producing useful germplasm, it is desirable to discover new genes that induce chromosomal variation. In this study, chromosome 5P from A.cristatum was shown to induce many types of chromosomal structural variation in a common wheat background, including nonhomoeologous chromosome translocations, as revealed by genomic in situ hybridization, fluorescence in situ hybridization, and DNA marker analysis. Aberrant meiosis was associated with chromosomal structural variation, and aberrant meiotic behavior was observed in wheat–A.cristatum 5P monosomic and disomic addition lines, suggesting that the effect of chromosome 5P was independent of the number of chromosome 5P copies. Chromosome 5P disturbed homologous chromosome pairing at pachytene stage in a common wheat background, resulting in a high frequency of univalent formation and reduced crossing over. Thirteen genes involved in DNA repair or chromatin remodeling, including RAD52-like and MSH6 genes, were differentially expressed(upregulated) in wheat–A. cristatum 5P addition lines according to transcriptome analysis, implicating chromosome 5P in the process of meiotic double-strand break repair. These findings provide a new, efficient tool for inducing wheat–alien chromosome translocations and producing new germplasm.

Development of P genome-specific SNPs and their application in tracing Agropyron cristatum introgressions in common wheat

As an important wild relative of wheat, Agropyron cristatum has been successfully used for wheat improvement. Currently, a few useful agronomic traits of A. cristatum, such as high grain number per spike and resistance to diseases, have been transferred into common wheat.However, the effective detection of small A. cristatum segmental introgressions in common wheat is still difficult. The objective of this study was to identify A. cristatum-specific single nucleotide polymorphisms(SNPs) for the detection of small alien segments in wheat. The transcriptome sequences of A. cristatum were aligned against wheat coding DNA sequences(CDS) for SNP calling. As a result, we discovered a total of 167,613 putative SNPs specific to the P genome of A. cristatum compared with the common wheat genomes. Among 230 selected SNPs with functional annotations related to inflorescence development and stress resistance,68 were validated as P genome-specific SNPs in multiple wheat backgrounds using Kompetitive Allele Specific PCR(KASP) assays. Among them, 55 SNPs were assigned to six homoeologous groups of the P genome using wheat-A. cristatum addition lines, and 6 P-specific SNP markers were further physically mapped on different segments of chromosome 6 P in 6 P translocation lines. The P genome-specific SNPs were also validated by Sanger sequencing and used to detect the P chromatin in wheat-A. cristatum cryptic introgression lines. Two SNP markers(Unigene20217-182 and Unigene20307-1420) were detected in two wheat-A. cristatum introgression lines that showed enhanced grain number per spike and high resistance to powdery mildew. Together, the developed P genome-specific SNP markers will accelerate the detection of large numbers of wheat-A. cristatum derivatives and will be helpful for marker-assisted transfer of desirable traits from A. cristatum into adapted wheat cultivars in wheat breeding programs.