Single R Gene Introgression Lines for Accurate Dissection of the Brassica - Leptosphaeria Pathosystem

Larkan, Nicholas J.; Yu, Fengqun; Lydiate, Derek J.; Rimmer, S. R.; Borhan, M. Hossein

doi:10.3389/fpls.2016.01771

Cited by 62 publications

(99 citation statements)

References 69 publications

(140 reference statements)

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“…A). As a positive control for the transformation, and to test for any further interference of AvrLm4–7 with R gene recognition, we tested the same transgenic isolates on B. napus Rlm3 control lines (Larkan et al ., ) and, as expected and reported previously (Plissonneau et al ., ), both AvrLm4–7 and AvrLm7 also suppressed the avirulence function of AvrLm3 (Table , Fig. A).…”

Section: Resultssupporting

confidence: 92%

“…Pathogen growth is blocked by the hypersensitive response of tissues at the margin of the infection site (dark brown ring) compared with a compatible response of Topas DH16516, showing the collapse of almost the entire cotyledon. Brassica napus differential lines Topas‐ Rlm3 , Topas‐ Rlm4 (Larkan et al ., ), Roxet and Goéland containing Rlm3 , Rlm4 , Rlm7 and Rlm9 resistance genes, respectively, were used as positive controls, and the susceptible B. napus cv. Topas DH16516 was used as a negative control.…”

Section: Resultsmentioning

confidence: 99%

“…One probable explanation for these exceptions could be related to errors in phenotyping the AvrLm9‐Rlm9 response on B. napus differential lines. We have observed this type of mis‐interpretation for pathotyping of Lm field isolates previously, particularly when the fungal inoculum does not display optimal vigour or the differential B. napus lines used in pathotyping are capable of generating weak non‐specific resistance responses (Larkan et al ., ). Now that the AvrLm9 gene has been cloned, the best approach to resolve conflicting phenotypic data would be to genotype the isolates with a questionable phenotype.…”

Section: Discussionmentioning

confidence: 97%

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Leptosphaeria maculans AvrLm9: a new player in the game of hide and seek with AvrLm4‐7

Ghanbarnia

Larkan

et al. 2018

Molecular Plant Pathology

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115

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Blackleg disease of Brassica napus caused by Leptosphaeria maculans (Lm) is largely controlled by the deployment of race-specific resistance (R) genes. However, selection pressure exerted by R genes causes Lm to adapt and give rise to new virulent strains through mutation and deletion of effector genes. Therefore, a knowledge of effector gene function is necessary for the effective management of the disease. Here, we report the cloning of Lm effector AvrLm9 which is recognized by the resistance gene Rlm9 in B. napus cultivar Goéland. AvrLm9 was mapped to scaffold 7 of the Lm genome, co-segregating with the previously reported AvrLm5 (previously known as AvrLmJ1). Comparison of AvrLm5 alleles amongst the 37 re-sequenced Lm isolates and transgenic complementation identified a single point mutation correlating with the AvrLm9 phenotype. Therefore, we renamed this gene as AvrLm5-9 to reflect the dual specificity of this locus. Avrlm5-9 transgenic isolates were avirulent when inoculated on the B. napus cultivar Goéland. The expression of AvrLm5-9 during infection was monitored by RNA sequencing. The recognition of AvrLm5-9 by Rlm9 is masked in the presence of AvrLm4-7, another Lm effector. AvrLm5-9 and AvrLm4-7 do not interact, and AvrLm5-9 is expressed in the presence of AvrLm4-7. AvrLm5-9 is the second Lm effector for which host recognition is masked by AvrLm4-7. An understanding of this complex interaction will provide new opportunities for the engineering of broad-spectrum recognition.

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Section: Resultssupporting

confidence: 92%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 97%

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Leptosphaeria maculans AvrLm9: a new player in the game of hide and seek with AvrLm4‐7

Ghanbarnia

Larkan

et al. 2018

Molecular Plant Pathology

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115

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“…The cultivars Excel and Roxet are Rlm7 cultivars that have been included in previous studies (Clarke et al ., ; Daverdin et al ., ; Larkan et al ., ). In the present study, results confirmed the presence of the Rlm7 genes in these cultivars; in addition, QR against L. maculans was detected in Excel and Roxet using the method of Huang et al .…”

Section: Discussionmentioning

confidence: 97%

Effectiveness of Rlm7 resistance against Leptosphaeria maculans (phoma stem canker) in UK winter oilseed rape cultivars

Mitrousia

Huang

et al. 2018

Plant Pathology

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The Rlm7 gene in Brassica napus is an important source of resistance for control of phoma stem canker on oilseed rape caused by the fungus Leptosphaeria maculans. This study shows the first report of L. maculans isolates virulent against Rlm7 in the UK. Leptosphaeria maculans isolates virulent against Rlm7 represented 3% of the pathogen population when cultivars with the Rlm7 gene represented 5% of the UK oilseed rape area in 2012/13. However, the Rlm7 gene has been widely used since then, representing >15% of the UK oilseed rape area in 2015/16. Winter oilseed rape field experiments included cultivars with the Rlm7 gene, with the Rlm4 gene or without Rlm genes and took place at five sites in the UK over four cropping seasons. An increase in phoma leaf spotting severity on Rlm7 cultivars in successive seasons was observed. Major resistance genes played a role in preventing severe phoma leaf spotting at the beginning of the cropping season and, in addition, quantitative resistance (QR) in the cultivars examined made an important contribution to control of phoma stem canker development at the end of the cropping season. Deployment of the Rlm7 resistance gene against L. maculans in cultivars with QR in combination with sustainable disease management practices will prolong the use of this gene for effective control of phoma stem canker epidemics.

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“…Canola ( B. napus ) breeding lines, Topas DH16516 (Topas-wild), a double haploid line susceptible to L. maculans and Topas -Rlm2 , an introgression line resistant to L. maculans isolates carrying AvrLm2 (Larkan et al, 2016a,b) were used as plant material. Seven-day old seedlings of both resistant and susceptible canola lines grown under controlled environment were point inoculated with pycnidiospores suspension of L. maculans isolate D5.…”

Section: Methodsmentioning

confidence: 99%

Comparative Transcriptomic Analysis of Virulence Factors in Leptosphaeria maculans during Compatible and Incompatible Interactions with Canola

et al. 2016

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Leptosphaeria maculans is a hemibiotrophic fungus that causes blackleg of canola (Brassica napus), one of the most devastating diseases of this crop. In the present study, transcriptome profiling of L. maculans was performed in an effort to understand and define the pathogenicity genes that govern both the biotrophic and the necrotrophic phase of the fungus, as well as those that separate a compatible from an incompatible interaction. For this purpose, comparative RNA-seq analyses were performed on L. maculans isolate D5 at four different time points following inoculation on susceptible cultivar Topas-DH16516 or resistant introgression line Topas-Rlm2. Analysis of 1.6 billion Illumina reads readily identified differentially expressed genes that were over represented by candidate secretory effector proteins, CAZymes, and other pathogenicity genes. Comparisons between the compatible and incompatible interactions led to the identification of 28 effector proteins whose chronology and level of expression suggested a role in the establishment and maintenance of biotrophy with the plant. These included all known Avr genes of isolate D5 along with eight newly characterized effectors. In addition, another 15 effector proteins were found to be exclusively expressed during the necrotrophic phase of the fungus, which supports the concept that L. maculans has a separate and distinct arsenal contributing to each phase. As for CAZymes, they were often highly expressed at 3 dpi but with no difference in expression between the compatible and incompatible interactions, indicating that other factors were necessary to determine the outcome of the interaction. However, their significantly higher expression at 11 dpi in the compatible interaction confirmed that they contributed to the necrotrophic phase of the fungus. A notable exception was LysM genes whose high expression was singularly observed on the susceptible host at 7 dpi. In the case of TFs, their higher expression at 7 and 11 dpi on susceptible Topas support an important role in regulating the genes involved in the different pathogenic phases of L. maculans. In conclusion, comparison of the transcriptome of L. maculans during compatible and incompatible interactions has led to the identification of key pathogenicity genes that regulate not only the fate of the interaction but also lifestyle transitions of the fungus.

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Single R Gene Introgression Lines for Accurate Dissection of the Brassica - Leptosphaeria Pathosystem

Cited by 62 publications

References 69 publications

Leptosphaeria maculans AvrLm9: a new player in the game of hide and seek with AvrLm4‐7

Leptosphaeria maculans AvrLm9: a new player in the game of hide and seek with AvrLm4‐7

Effectiveness of Rlm7 resistance against Leptosphaeria maculans (phoma stem canker) in UK winter oilseed rape cultivars

Comparative Transcriptomic Analysis of Virulence Factors in Leptosphaeria maculans during Compatible and Incompatible Interactions with Canola

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