Molecular cytogenetic characterization of a new wheat-rye 1BL•1RS translocation line expressing superior stripe rust resistance and enhanced grain yield

Main conclusion

A new wheat-rye 1BL?1RS translocation line, with the characteristics of superior stripe rust resistance and high thousand-kernel weight and grain number per spike, was developed and identified from progenies of wheat-rye- Psathyrostachys huashanica trigeneric hybrids.

Abstract

The wheat-rye 1BL?1RS translocation line from Petkus rye has contributed substantially to the world wheat production. However, due to extensive growing of cultivars with disease resistance genes from short arm of rye chromosome 1R and coevolution of pathogen virulence and host resistance, these cultivars successively lost resistance to pathogens. In this study, a new wheat-rye line K13-868, derived from the progenies of wheat-rye-Psathyrostachys huashanica trigeneric hybrids, was identified and analyzed using fluorescence in situ hybridization (FISH), genomic in situ hybridization (GISH), acid polyacrylamide gel electrophoresis (A-PAGE), and molecular markers. Cytological studies indicated that the mean chromosome configuration of K13-868 at meiosis was 2n = 42 = 0.14 I + 18.78 II (ring) + 2.15 II (rod). Sequential FISH and GISH results demonstrated that K13-868 was a compensating wheat-rye 1BL?1RS Robertsonian translocation line. Acid PAGE analysis revealed that clear specific bands of rye 1RS were expressed in K13-868. Simple sequence repeat (SSR) and rye 1RS-specific markers ω-sec-p1/ω-sec-p2 and O-SEC5′-A/O-SEC3′-R suggested that the 1BS arm of wheat had been substituted by the 1RS arm of rye. At the seedling and adult growth stage, compared with its recurrent wheat parent SM51 and six other wheat cultivars containing the 1RS arm in southwestern China, K13-868 showed high levels of resistance to stripe rust (Puccinia striiformis f. sp. tritici, Pst) pathogens prevalent in China, which are virulent to Yr10 and Yr24/Yr26. In addition, K13-868 expresses higher thousand-kernel weight and more grain number per spike than these controls in two growing seasons, suggesting that this line may carry yield-related genes of rye. This translocation line, with significant characteristics of resistance to stripe rust and high thousand-kernel weight and grain number per spike, could be utilized as a valuable germplasm for wheat improvement.

     

Molecular and computational approaches to understand resistance of New Delhi metallo β-lactamase variants (NDM-1, NDM-4, NDM-5, NDM-6, NDM-7)-producing strains against carbapenems

The discovery of NDM-1 and its variants has caused the emergence of antibiotic resistance in the community and hospital setting, causing major concern for health care across the globe. New Delhi Metallo-β-lactamase is known to hydrolyse almost all β-lactam antibiotics. Studies have shown the hydrolytic activates of NDM-1 and some of its variants, however a comparative study of these NDM variants has not been explored in detail. Hence, we proposed to check their catalytic activity by performing a comparative study between NDM-1 and its variants. The study was initiated to clone NDM variants (NDM-1, NDM-4, NDM-5, NDM-6 and NDM-7) followed by overexpression of the recombinant proteins to check their hydrolytic properties against β-lactam antibiotics. The minimum inhibitory concentration of carbapenems antibiotics for bla_NDM-5 clone was found four fold increased, whereas no change was observed in the clones having other variants. The hydrolytic activity of carbapenem with NDM-5 variant was found to be augmented as per the kinetics parameter where Km was decreased and kcat, kcat/Km values increased as compared to the NDM-1. Molecular docking studies were employed to identify the variations in the binding ability among all NDM variants with imipenem or meropenem. Simulation studies at 100?ns showed a good stability of NDM-5 with imipenem and meropenem as compared to NDM-1. CD spectroscopy data revealed significant changes in the secondary structure of NDM variants. We conclude that NDM-5 showed higher hydrolytic activity as compared to other variants. This study provides a comparative analysis of the severity of NDM producing strains.     

A linkage map of the chickpea (Cicer arietinum L.) genome based on recombinant inbred lines from a C. arietinum×C. reticulatum cross: localization of resistance genes for fusarium wilt races 4 and 5

An integrated molecular marker map of the chickpea genome was established using 130 recombinant inbred lines from a wide cross between a cultivar resistant to fusarium wilt caused by Fusarium oxysporum Schlecht. emend. Snyd. &. Hans f. sp. ciceri (Padwick) Snyd & Hans, and an accession of Cicer reticulatum (PI 489777), the wild progenitor of chickpea. A total of 354 markers were mapped on the RILs including 118 STMSs, 96 DAFs, 70 AFLPs, 37 ISSRs, 17 RAPDs, eight isozymes, three cDNAs, two SCARs and three loci that confer resistance against different races of fusarium wilt. At a LOD-score of 4.0, 303 markers cover 2077.9 cM in eight large and eight small linkage groups at an average distance of 6.8 cM between markers. Fifty one markers (14.4%) were unlinked. A clustering of markers in central regions of linkage groups was observed. Markers of the same class, except for ISSR and RAPD markers, tended to generate subclusters. Also, genes for resistance to races 4 and 5 of fusarium wilt map to the same linkage group that includes an STMS and a SCAR marker previously shown to be linked to fusarium wilt race 1, indicating a clustering of several fusarium-wilt resistance genes around this locus. Significant deviation from the expected 1 : 1 segregation ratio was observed for 136 markers (38.4%, P<0.05). Segregation was biased towards the wild progenitor in 68% of the cases. Segregation distortion was similar for all marker types except for ISSRs that showed only 28.5% aberrant segregation. The map is the most extended genetic map of chickpea currently available. It may serve as a basis for marker-assisted selection and map-based cloning of fusarium wilt resistance genes and other agronomically important genes in future. Received: 17 November 1999 / Accepted: 4 June 2000