Contribution of Duplicated Nucleotide-Binding Leucine-Rich Repeat (NLR) Genes to Wheat Disease Resistance.

Wheat has a large and diverse repertoire of NLRs involved in disease resistance, with over 1500 NLRs detected in some studies. These NLR genes occur as singletons or clusters containing copies of NLRs from different phylogenetic clades. The number of NLRs and cluster size can differ drastically among ecotypes and cultivars. Primarily, duplication has led to the evolution and diversification of NLR genes. Among the various mechanisms, whole genome duplication (WGD) is the most intense and leading cause, contributing to the complex evolutionary history and abundant gene set of hexaploid wheat. Tandem duplication or recombination is another major mechanism of NLR gene expansion in wheat. The diversity and divergence of duplicate NLR genes are responsible for the broad-spectrum resistance of most plant species with limited R genes. Understanding the mechanisms underlying the rapid evolution and diversification of wheat NLR genes will help improve disease resistance in crops. The present review focuses on the diversity and divergence of duplicate NLR genes and their contribution to wheat disease resistance. Moreover, we provide an overview of disease resistance-associated gene duplication and the underlying strategies in wheat.

Genetic architecture and candidate gene identification for grain size in bread wheat by GWAS.

Grain size is a key trait associated with bread wheat yield. It is also the most frequently selected trait during domestication. After the phenotypic characterization of 768 bread wheat accessions in three plots for at least two years, the present study shows that the improved variety showed significantly higher grain size but lower grain protein content than the landrace. Using 55K SNP assay genotyping and large-scale phenotyping population and GWAS data, we identified 5, 6, 6, and 6 QTLs associated with grain length, grain weight, grain area, and thousand grain weight, respectively. Seven of the 23 QTLs showed common association within different locations or years. Most significantly, the key locus associated with grain length, qGL-2D, showed the highest association after years of multi-plot testing. Haplotype and evolution analysis indicated that the superior allele of qGL-2D was mainly hidden in the improved variety rather than in landrace, which may contribute to the significant difference in grain length. A comprehensive analysis of transcriptome and homolog showed that TraesCS2D02G414800 could be the most likely candidate gene for qGL-2D. Overall, this study presents several reliable grain size QTLs and candidate gene for grain length associated with bread wheat yield.

Wheat-Thinopyrum Substitution Lines Imprint Compensation Both From Recipients and Donors.

Even frequently used in wheat breeding, we still have an insufficient understanding of the biology of the products via distant hybridization. In this study, a transcriptomic analysis was performed for six Triticum aestivum-Thinopyrum elongatum substitution lines in comparison with the host plants. All the six disomic substitution lines showed much stronger "transcriptomic-shock" occurred on alien genomes with 57.43-69.22% genes changed expression level but less on the recipient genome (2.19-8.97%). Genome-wide suppression of alien genes along chromosomes was observed with a high proportion of downregulated genes (39.69-48.21%). Oppositely, the wheat recipient showed genome-wide compensation with more upregulated genes, occurring on all chromosomes but not limited to the homeologous groups. Moreover, strong co-upregulation of the orthologs between wheat and Thinopyrum sub-genomes was enriched in photosynthesis with predicted chloroplastic localization, which indicates that the compensation happened not only on wheat host genomes but also on alien genomes.