Stripe rust (yellow rust), caused by Puccinia striiformis f. sp. tritici, is one of the most devastating foliar diseases of wheat (Triticum aestivum) worldwide. Growing resistant cultivars is the best approach for control of the disease. Although the stripe rust resistance in spring wheat cv. Zak has been circumvented by a group of races of the pathogen predominant in the United States since 2000, the resistance genes in Zak were unknown. To identify and map the genes for resistance to stripe rust, Zak was crossed with susceptible wheat genotype 'Avocet Susceptible'. Seedlings of the parents and F1, F2, and F3 progeny were tested with P. striiformis f. sp. tritici races PST-43 and PST-45 under controlled greenhouse conditions. Genetic analysis determined that Zak has a single dominant gene, designated as YrZak, conferring race-specific all-stage resistance. Resistance gene analog polymorphism (RGAP), simple sequence repeat (SSR), and sequence-tagged site (STS) techniques were used to identify molecular markers linked to YrZak. A linkage group of three RGAP, three SSR, and three STS markers was constructed for YrZak using 205 F3 lines. Amplification of the complete set of Chinese Spring nulli-tetrasomic lines with RGAP marker Xwgp102 indicated that YrZak is present on chromosome 2B. The three SSR markers further mapped YrZak to the long arm of chromosome 2B. Amplification of chromosome 2B deletion lines with SSR marker Xgwm501 further confirmed that YrZak is on chromosome 2BL. To determine the genetic distance between YrZak and Yr5, which also is present on chromosome 2BL, 300 F2 plants from cross Zak/Yr5 were tested with PST-43. Six susceptible plants were identified from the F2 population, indicating that YrZak and Yr5 are approximately 42 centimorgans apart. The results of race reactions and chromosomal locations indicated that YrZak is different from previously identified genes for resistance to stripe rust. This gene should be useful in monitoring virulence changes in the pathogen population and in studying host-pathogen interactions.
In this study, a gene with a full-length cDNA of 1422 bp encoding 473 amino acids, designated RrGT2, was isolated from R. rugosa ‘Zizhi’ and then functionally characterized. RrGT2 transcripts were detected in various tissues and were proved that their expression patterns corresponded with anthocyanins accumulation. Functional verification of RrGT2 in R. rugosa was performed via VIGS. When RrGT2 was silenced, the Rosa plants displayed a pale petal color phenotype. The detection results showed that the expression of RrGT2 was significantly downregulated, which was consistent with the decrease of all anthocyanins; while the expression of six key upstream structural genes was normal. Additionally, the in vivo function of RrGT2 was investigated via its overexpression in tobacco. In transgenic tobacco plants expressing RrGT2, anthocyanin accumulation was induced in the flowers, indicating that RrGT2 could encode a functional GT protein for anthocyanin biosynthesis and could function in other species. The application of VIGS in transgenic tobacco resulted in the treated tobacco plants presenting flowers whose phenotypes were lighter in color than those of normal plants. These results also validated and affirmed previous conclusions. Therefore, we speculated that glycosylation of RrGT2 plays a crucial role in anthocyanin biosynthesis in R. rugosa.
At present, the research about flower color of Rosa rugosa is a very innovative and practical study. Glycosylation modification fulfills an important role in increasing the stability and solubility of anthocyanin in plants. In this study, based on the transcriptional database of R. rugosa, a gene with full length cDNA of 1422bp, encoding 473 amino acids, designated as RrGT2, were isolated from flowers of R. rugosa 'Zizhi' and then functionally characterized. According to online software prediction, the molecular formula of the protein encoded by the RrGT2 gene is C 2334 H 3628 N 602 O 711 S 18 , the relative molecular mass is 52,075.17 Da, and the theoretical isoelectric point is pI = 4.76. The result of the RrGT2 protein 3D model construction showed that it had the highest homology with the UDP-glycosyltransferase 74F2 protein model in the database (39.53%). Sequence alignments with the NCBI database showed that the RrGT2 protein is a member of the GTB superfamily. Homology analysis revealed that the coding regions of RrGT2 was highly specific among different species, but still had typical conserved amino acid residues called PSPG that are crucial for RrGT2 enzyme activity. RrGT2 transcripts were detected in five flowering stages and seven tissues of R. rugosa 'Zizhi', R. rugosa 'Fenzizhi' and R. rugosa 'Baizizhi', and their expression patterns corresponded with the accumulation of anthocyanins. Therefore, we speculated that glycosylation of RrGT2 plays a crucial role in anthocyanin biosynthesis in R. rugosa.
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