Browsing by Author "Tabe, Linda"

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Cellular and molecular characterization of a stem rust resistance locus on wheat chromosome 7AL
(2016-12) Pujol, Vincent; Robles, Jose; Wang, Penghao; Taylor, Jen; Zheng, Peng; Huang, Li; Tabe, Linda; Lagudah, Evans
"BACKGROUND: Wheat stem rust, caused by Puccinia graminis f. sp. tritici, is a major wheat disease which is mainly controlled through the release of resistant cultivars containing one or several resistance genes. Considerable effort has been put into the discovery of new resistance genes, but knowledge of their mechanisms of action is often lacking. In this study, the mechanism of resistance conferred by a recently discovered stem rust resistance locus on wheat chromosome 7AL was investigated through microscopic observations and RNA-sequencing, using the susceptible line Columbus and the independent, backcrossed, resistant lines Columbus-NS765 and Columbus-NS766. RESULTS: Microscopic observations of infected leaves revealed that the resistance conferred by the 7AL resistance locus was initiated 2 days post-inoculation, upon the fungus entry into the plant through the stoma. Resistance was manifested by death of guard and epidermal cells adjacent to an infection site. Occasionally, similar observations were made in the susceptible line, suggesting that the resistance response was the same in all genotypes, but enhanced in the resistant lines. Transcriptomic analysis, combined with assignment of genes to wheat chromosomes, revealed a disproportionately high number of differentially expressed genes were located on chromosomes 7AL and 6A. A number of genes annotated as cysteine-rich receptor-like kinases were located on chromosome 7AL. Closer investigation indicated that the encoded proteins were in fact putative receptor-like cytoplasmic kinases. One of the putative RLCK genes contained a SNP marker previously shown to co-segregate with the 7AL resistance locus. The results also indicated the presence of a large introgression on chromosome 6A in both resistant lines, but whether it has any role in the resistance response is unclear. CONCLUSIONS: This study represents the first investigation on the resistance mechanism conferred by the wheat 7AL stem rust resistance locus. The resistance response was associated with pre-haustorial cell death, and the transcriptome analysis suggested putative receptor-like cytoplasmic kinases as candidate resistance genes for further investigation."
Wheat mutant MNR220 delays haustoria formation during leaf rust pathogenesis at the seedling stage
(2016-09) Talajoor, Mina R.; Wang, Xiaojing; Zhang, Hongtao; Zhang, Peng; Bhavani, Sridhar; Tabe, Linda; Lagudah, Evans; Huang, Li
This study reports further characterization of the defence mechanism of an EMS-induced mutant (MNR220) that displays enhanced resistance to leaf rust, stem rust, stripe rust and powdery mildew diseases. The broad-spectrum resistance of the mutant was characterized by a microscopy study and additional race screenings of two rust pathogens. The mutant displayed less disease severity in response to all the races tested, when compared with the wild-type. The microscopy study of the pathogenesis of a leaf rust race PBJJG on the mutant revealed that the resistance was first evident at the pre-haustorial stage; formation of haustoria was significantly delayed or inhibited in the mutant compared with the wild-type. The mutant displayed microscopic level of cell death even in the absence of any pathogens. These findings suggest that MNR220 mediates a spontaneous cell death that delays the infection process by delaying haustoria formation of the pathogen.