Wheat leaf rust, caused by Puccinia triticina, is a severe fungal disease threatening global wheat production. The rational application of genetic loci controlling wheat resistance to leaf rust in breeding practice is still the best choice for disease control. A previous study indicated that the Argentinean wheat cultivar “Klein Proteo” might carry leaf rust resistance (Lr) genes Lr3a and Lr10, as well as an unknown Lr gene. In this study, seedlings of “Klein Proteo” showed high resistance to all the 20 Pt pathotypes isolated in China. Using bulked segregant RNA sequencing (BSR-seq) and developed CAPS markers, the single-dominant gene LrKP was initially mapped to a 114–168 Mb region on chromosome 2BS. Using gene-specific primers of a previously cloned chromosome 2BS-located Lr13 gene, we found that “Klein Proteo” also carried the Lr13 gene. Moreover, the expression of Lr13 in the resistant bulk was significantly higher than that in the susceptible bulk. Nevertheless, “Klein Proteo” showed a much broader and higher resistance compared with the near isogenic line and “ZhouMai 22” carrying Lr13. In conclusion, the wheat cultivar “Klein Proteo” showed great potential in the genetic improvement of wheat resistance to leaf rust in China and the genetic bases controlling the broad-spectrum resistance were initially revealed.
Einkorn wheat (Triticum monococcum) is one of the oldest cereal crops to be domesticated by human beings, playing essential role in early agriculture development. Today, it is considered an important genomic resource for modern wheat improvement, especially for resistance against pests and diseases. However, the exploration and utilization of useful genes from T. monococcum is limited due to the lack of a reference genome and annotation for this species. Here, we report a near-complete genome assembly for T. monococcum with a total length of 5.11 Gb with a contig N50 of 131.2Mb and scaffold N50 of 728.66Mb, representing a genome assembly of highest quality for any wheat genome reported. Phylogenomic analysis confirmed T. monococcum is closely-related to T. urartu, the progenitor of wheat A subgenomes. A 4AL/5AL terminal translocation is present in the diploid species T. urartu and T. monococcum, taking place before wheat polyploidization. T. monococcum has significantly expanded and unique gene families involved in DNA damage repair and heat stress tolerance, reflecting its adaptive evolution to cope with historical harsh climate in its natural habitat, South East Turkey. The genome sequence confirmed the introgression of T. monococcum rust resistance genes at 5AmL into modern bread wheat varieties. This near-complete reference genome of T. monococcum will be an essential resource for wheat functional and evolutionary genomic studies and expedite the cloning of useful genes in T. monococcum for future wheat improvement. Keywords: Triticum monococcum, reference genome, genome rearrangement, resistance genes, stem and leaf rust, PacBio HiFi sequencing
Key message The diploid wheat recessive stem rust resistance gene SrTm4 was fine-mapped to a 754-kb region on chromosome arm 2AmL and potential candidate genes were identified. Abstract Race Ug99 of Puccinia graminis f. sp. tritici (Pgt), the causal agent of wheat stem (or black) rust is one of the most serious threats to global wheat production. The identification, mapping, and deployment of effective stem rust resistance (Sr) genes are critical to reduce this threat. In this study, we generated SrTm4 monogenic lines and found that this gene confers resistance to North American and Chinese Pgt races. Using a large mapping population (9522 gametes), we mapped SrTm4 within a 0.06 cM interval flanked by marker loci CS4211 and 130K1519, which corresponds to a 1.0-Mb region in the Chinese Spring reference genome v2.1. A physical map of the SrTm4 region was constructed with 11 overlapping BACs from the resistant Triticum monococcum PI 306540. Comparison of the 754-kb physical map with the genomic sequence of Chinese Spring and a discontinuous BAC sequence of DV92 revealed a 593-kb chromosomal inversion in PI 306540. Within the candidate region, we identified an L-type lectin-domain containing receptor kinase (LLK1), which was disrupted by the proximal inversion breakpoint, as a potential candidate gene. Two diagnostic dominant markers were developed to detect the inversion breakpoints. In a survey of T. monococcum accessions, we identified 10 domesticated T. monococcum subsp. monococcum genotypes, mainly from the Balkans, carrying the inversion and showing similar mesothetic resistant infection types against Pgt races. The high-density map and tightly linked molecular markers developed in this study are useful tools to accelerate the deployment of SrTm4-mediated resistance in wheat breeding programs.
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