| The gene Yr26 confers resistance to yellow rust caused by Puccinia triticina(Puccinia striiformis f. sp. tritici.) in wheat. The isolation of Yr26 and yellow rust resistance-related genes will play an important role in future disease resistant breeding. Ma et al. mapped Yr26 on the short arm of 1B. Here, 23 resistance-related ESTs physically mapped to 1S were chosen for sequenced-tagged site (STS) primer design. None of the PCR products revealed polymorphisms between susceptible and resistant parents Yangmai 5 and 92R137 as well as susceptible and resistant pools using these primers. PCR products amplified by BE446250-derived primer were digested with the restriction enzyme HaeⅢand a polymorphic band specific to the susceptible lines was observed. RT-PCR was conducted on cDNA templates by nest primers derived from the same EST, and the 283bp, 296bp cDNA fragments were isolated from Yangmai 5 and 92R137, respectively. Southern blot using the 296bp fragment as probe detected a specific hybridization band in resistant lines.A positive clone from chromosome 1DS was selected from the TAC library of wheat-H. villosa 6VS/6AL translocation line 92R137 by PCR using primer BE446250. A partial fragment was sequenced from the positive clone and was used to develop new primers. Only primer BX-10 amplified a polymorphic band linked to the resistance gene Yr26. Analysis of a F2 population (Yangmai 5×92R137) showed that this marker is 2.7cM distal to the locus of Yr26. The sequence of the polymorphic band had more than 90% homology to three resistance gene-like sequence from barley and had significant homology to NB-ARC domain existed in several genes for disease resistance.Gene RAR1, SGT1 conserved in eukaryotes and multiple R protein-mediated resistance required for either one of them or both. Specific primers were designed according to wheat ESTs which are highly homologous to barley RAR1, SGT1 genes. These specific primers were used for RT-PCR, and the full-length of Ta-RAR1, Ta-SGT1 cDNA sequence were isolated in combination with RACE technique. The amino acid sequence of Ta-RAR1, Ta-SGT1 shared 97%, 93% identity with those of barley (Hordeum vulgare), respectively. Bombardment mediated transient expression analysis of a chimeric CaMV 35S: Ta-RAR1-GFP construct showed that the protein mainly targeted to membrane in onion epidermal cell.Transcription patterns of Ta-RAR1 and Ta-SGT1 were investigated after inoculation with yellow rust pathogen through semi-quantitative RT-PCR. The results showed that the transcriptional level of Ta-RAR1 was enhanced at about 24h post-inoculation in both resistant and susceptible parents. But the expression of Ta-SGT1 was not induced in wheat by yellow rust pathogen. The results of semi-quantitative RT-PCR showed that the expression of RAR1, SGT1 both increased in powdery mildew resistance Haynaldia.villosa leaves when inoculated by powdery mildew (Erysiphe graminis D. C. ex Merat Esp. tritici). The fragments of Ta-RAR1, Ta-SGT1 have been constructed to BSMV-derived virus-induced gene sliencing vectors, and would be used to further study whether these two genes involve the Yr26, Pm21-mediated resistance pathway in wheat.
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