Isolation And Mapping Of Resistance Homology Sequences Related To Yr26Gene In Wheat

Wheat （Triticum aestivum L.） is an important crop and a primary food source forhumans.Stripe rust is an important disease of wheat, which caused by the fungal pathogenPuccinia striiformis. f. sp. tritici （Pst）. The approachs to control the disease, which is themost economical, effective and environment, is growing resistant cultivars. However, thespeed of traditional breeding often lags behind the physiological races of Puccinia striiformisrate. Cloning of resistance genes in wheat may contribute to understanding the mechanism ofresistance at the molecular level and to a better understanding of the gene and its possiblealleles, but also speed up the process of molecular breeding.The Yr26gene, which is present in the common wheat line92R137, was derived fromChinese T.turgidum landrace γ80-1. Wheat variety92R137, developed by the CytogeneticsInstitute of Nanjing Agricultural University, shows high resistance to stripe rust and powderymildew germplasm in both seedling and adult-plant stage in China. Stripe rust resistance geneYr26to and powdery mildew resistance gene Pm21both located on the1B chromosome.In this study, NBS-LRR class resistance gene homology fragments from wheat wereisolated using homology-based method and nested-PCR technology, and relationships withwheat stripe rust resistance gene Yr26were validated. The results obtained are as follows:1. Resistance cultivars lines,92R137, carrying of Yr26gene; susceptible cultivarYangmai158, Yr26NILs Nan137（Yangmai158/6Yr26） containing Yr26gene. Thesematerials were used to identify the resistance to stripe rust and powdery mildew in seedlingstage. Results showed that Nan137was resistance （reaction1） and Yangmai158wassusceptible （reaction9） to wheat stripe rust CY32. Nan137and susceptible parent Yangmai158inoculated of wheat powdery mildew Guanzhong4, the identification results showedNan137was high resistance to wheat powdery mildew, but Yangmai158was highlysusceptible.2. A6F₁, F₂population of196plants and145F₃line progenies with30–40plants ineach, derived from a cross between susceptible genotype Avocet S （AvS） and resistant line92R137（Yr26）. Wheat stripe rust races32（CYR32） were used to identify resistance tostripe rust on each generation plant. Seedlings of92R137were resistant and those of AvSwere susceptible in a seedling test for race CYR32.The6F₁plants were resistant.196plantsof F₂population segregated with145resistant plants and51susceptible plants, fitting a3:1 ratio （χ²3:1=0.109＜3.84）, indicating that Yr26in the AvS×92R137population behaved as asingle dominant gene to confirm the phenotypes of the corresponding F₂plants. Among the F₃families tested with the same race,46of145families derived from resistant F₂plants werehomozygous resistant,99segregated and51families derived from susceptible F₂plants werehomozygous susceptible. Segregation of these families conformed to a1:2:1ratio （χ²1:2:1=0.28, df=2） as expected for a single gene.3. Primers were designed based on the conserved domains of the cloned plant diseaseresistance genes, and the nested PCR was used to isolate resistance gene homology fragmentsfrom Nan137.Four open-reading resistance gene analogues （RGAs） were obtained, i.e.,R105、R181、R326and R405. The nucleotide sequences of the four RGAs were369bp,589bp,528bp and618bp. Homology research showed that the four fragments had typical conservedregions NBS-LRR, and the nucleotide identity of four fragments was from24.35%to38.36%.And the four fragments were successfully transformed into STS marker: STSR105、STSR181、STSR326、STSR405. Phylogenetic tree analysis based on the alignment of the deduced amino-acidsequences of the four RGAs in wheat and the16cloned R genes shows that R105and RPR1,R181and RPP1-WsB, R326、M and L6, R405and N had close genetic relationship.4. The fragments were localized by Chinese Spring （CS） deletion lines of chromosome1B（1BS-10-0.50,1BS-9-0.84,1BS-10-0.50,1BL-1-0.47and1BL-2-0.69）, F₂:3populationsderived from susceptible cultivar Avocet S and the lines92R137carrying Yr26were used toevaluate the relationship between the isolated RGAs and Yr26gene. Only R405was mappedin the deletion bin C-1BL-0.6-0.32with Chinese Spring deletion lines and was co-segregatedwith a F₂population of196plants. Thus, R405was mapped in the Yr26region andco-segregated with Yr26, we initially hypothesized that the R405might be the candidatesequence of Yr26, which provides a good prerequisite for further study.