Browsing by Author "Carstens, Maryke"

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    Increased resistance to biotrophic pathogens in the Arabidopsis constitutive induced resistance 1 mutant is EDS1 and PAD4-dependent and modulated by environmental temperature
    (Public Library of Science, 2014) Carstens, Maryke; McCrindle, Tyronne K; Adams, Nicolette; Diener, Anastashia; Guzha, Delroy T; Murray, Shane L; Parker, Jane E; Denby, Katherine J; Ingle, Robert A
    The Arabidopsis constitutive induced resistance 1 ( cir1 ) mutant displays salicylic acid (SA)-dependent constitutive expression of defence genes and enhanced resistance to biotrophic pathogens. To further characterise the role of CIR1 in plant immunity we conducted epistasis analyses with two key components of the SA-signalling branch of the defence network, ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1) and PHYTOALEXIN DEFICIENT4 (PAD4). We demonstrate that the constitutive defence phenotypes of cir1 require both EDS1 and PAD4, indicating that CIR1 lies upstream of the EDS1-PAD4 regulatory node in the immune signalling network. In light of this finding we examined EDS1 expression in cir1 and observed increased protein, but not mRNA levels in this mutant, suggesting that CIR1 might act as a negative regulator of EDS1 via a post-transcriptional mechanism. Finally, as environmental temperature is known to influence the outcome of plant-pathogen interactions, we analysed cir1 plants grown at 18, 22 or 25°C. We found that susceptibility to Pseudomonas syringae pv. tomato ( Pst ) DC3000 is modulated by temperature in cir1 . Greatest resistance to this pathogen (relative to PR-1:LUC control plants) was observed at 18°C, while at 25°C no difference in susceptibility between cir1 and control plants was apparent. The increase in resistance to Pst DC3000 at 18°C correlated with a stunted growth phenotype, suggesting that activation of defence responses may be enhanced at lower temperatures in the cir1 mutant.
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    Understanding the mechanisms of cir1 disease resistance in Arabidopsis thaliana
    (2008) Carstens, Maryke; Denby, Katherine J; Illing, Nicola
    Plants have evolved an elaborate and very effective defence system to curb disease caused by pathogen infections. To gain insight into the defence signalling network and defence responses deployed by plants for resistance to pathogens, the defence-related Arabidopsis thaliana mutant cir1 (constitutively induced resistance 1) was further investigated. It was previously shown that cir1 constitutively expresses salicylic acid-, jasmonic acid- and ethylene-dependent defence-related genes and exhibits increased resistance to the virulent bacterial pathogen Pseudomonas syringae pv. tomato and the virulent oomycete pathogen Hyaloperonospora parasitica Noco2. Through first–pass mapping experiments, it was formerly determined that the CIR1 locus is located on the lower arm of chromosome IV. With the aim of identifying the CIR1 gene, comprehensive genomic mapping of cir1 was conducted in this study. Upon the generation of a suitable mapping population, PCR-based markers were employed to narrow down CIR1 location to 309.10 kb. This region was included in six genomic DNA clones which were tested for complementation of the cir1 mutant. A small region in which CIR1 resides was identified and possible candidate genes within it were investigated. It was established that CIR1 is one of eight annotated genes. This study also assessed which known components of the defence signalling network play a role in cir1-mediated resistance, to establish a possible function of CIR1 in the Arabidopsis defence network. Epistasis analyses were performed between cir1 and the eds1 (enhanced disease susceptibility 1) and pad4 (phytoalexin deficient 4) mutants which regulate the salicylic acid signalling pathway, as well as the coi1 (coronatine-insensitive 1) mutant which functions in the jasmonic acid signalling pathway. The disease resistance profiles of cir1 eds1, cir1 pad4 and cir1 coi1 double mutants to infection by virulent P. syringae and virulent H. parasitica established that coi1, pad4 and eds1 are epistatic to cir1, suggesting that CIR1 is located upstream in the defence signalling network. Through defence-related gene expression profiling, it was found that cir1 simultaneously activates multiple signalling pathways, resulting in the induced expression of many defence-related genes and the increased expression of some of these genes was correlated to cir1’s enhanced resistance to virulent pathogens. Therefore, it appears that CIR1 functions as a negative regulator of the disease resistance signalling network. Furthermore, EDS1 protein accumulation may play a role in cir1-mediated resistance as it was found that cir1 has a stabilizing effect on the EDS1 protein.