scholarly journals Albugo candida (white rust) suppresses resistance to downy mildew pathogens in Arabidopsis thaliana

2017 ◽  
Vol 38 (SI 2 - 6th Conf EFPP 2002) ◽  
pp. 474-476 ◽  
Author(s):  
A.J. Cooper ◽  
A. Woods-Tör ◽  
E.B. Holub
Keyword(s):  
Arabidopsis Thaliana ◽  
Downy Mildew ◽  
Rust Resistance ◽  
Downy Mildew Resistance ◽  
Bremia Lactucae ◽  
Structural Class ◽  
Albugo Candida ◽  
White Rust ◽  
Downy Mildews ◽  
Hyaloperonospora Parasitica

Arabidopsis thaliana accessions were inoculated with incompatible isolates of downy mildews, following pre-inoculation with compatible Albugo candida. Three isolates of Hyaloperonospora parasitica subsp. A. thaliana, an isolate of H. parasitica subsp. Brassica oleracea and one Bremia lactucae (lettuce) isolate were included. All downy mildews sporulated on A. thaliana, suggesting A. candida suppresses broad-spectrum downy mildew resistance. The white rust resistance gene, RAC5, is being investigated. The resistance phenotype associated with RAC5 seems not to involve a hypersensitive response. RAC5 has been mapped telomeric of nga106 on chromosome 5, in a region lacking NB-LRR genes, the most common structural class of resistance genes known in A. thaliana.

scholarly journals WRR4 Encodes a TIR-NB-LRR Protein That Confers Broad-Spectrum White Rust Resistance in Arabidopsis thaliana to Four Physiological Races of Albugo candida

2008 ◽  
Vol 21 (6) ◽  
pp. 757-768 ◽  
Author(s):  
M. Hossein Borhan ◽  
Nick Gunn ◽  
Abigail Cooper ◽  
Sigrun Gulden ◽  
Mahmut Tör ◽  
...  
Keyword(s):  
Arabidopsis Thaliana ◽  
Broad Spectrum ◽  
Rust Resistance ◽  
Functional Expression ◽  
Oilseed Crop ◽  
Transgenic Expression ◽  
Albugo Candida ◽  
Physiological Races ◽  
White Rust ◽  
Race 4

White blister rust in the Brassicaceae is emerging as a superb model for exploring how plant biodiversity has channeled speciation of biotrophic parasites. The causal agents of white rust across a wide breadth of cruciferous hosts currently are named as variants of a single oomycete species, Albugo candida. The most notable examples include a major group of physiological races that each are economically destructive in a different vegetable or oilseed crop of Brassica juncea (A. candida race 2), B. rapa (race 7), or B. oleracea (race 9); or parasitic on wild crucifers such as Capsella bursa-pastoris (race 4). Arabidopsis thaliana is innately immune to these races of A. candida under natural conditions; however, it commonly hosts its own molecularly distinct subspecies of A. candida (A. candida subsp. arabidopsis). In the laboratory, we have identified several accessions of Arabidopsis thaliana (e.g.,. Ws-3) that can permit varying degrees of rust development following inoculation with A. candida races 2, 4, and 7, whereas race 9 is universally incompatible in Arabidopsis thaliana and nonrusting resistance is the most prevalent outcome of interactions with the other races. Subtle variation in resistance phenotypes is evident, observed initially with an isolate of A. candida race 4, indicating additional genetic variation. Therefore, we used the race 4 isolate for map-based cloning of the first of many expected white rust resistance (WRR) genes. This gene was designated WRR4 and encodes a cytoplasmic toll-interleukin receptor-like nucleotide-binding leucine-rich repeat receptor-like protein that confers a dominant, broad-spectrum white rust resistance in the Arabidopsis thaliana accession Columbia to representative isolates of A. candida races 2, 4, 7, and 9, as verified by transgenic expression of the Columbia allele in Ws-3. The WRR4 protein requires functional expression of the lipase-like protein EDS1 but not the paralogous protein PAD4, and confers full immunity that masks an underlying nonhypersensitive incompatibility in Columbia to A. candida race 4. This residual incompatibility is independent of functional EDS1.

scholarly journals Mutants of downy mildew resistance in Lactuca sativa (lettuce).

Genetics ◽  
1994 ◽  
Vol 137 (3) ◽  
pp. 867-874
Author(s):  
P A Okubara ◽  
P A Anderson ◽  
O E Ochoa ◽  
R W Michelmore
Keyword(s):  
Molecular Marker ◽  
Downy Mildew ◽  
Genomic Dna ◽  
Spontaneous Mutation ◽  
Multigene Families ◽  
Downy Mildew Resistance ◽  
Bremia Lactucae ◽  
Wild Type ◽  
Mildew Resistance ◽  
Recessive Mutations

Abstract As part of our investigation of disease resistance in lettuce, we generated mutants that have lost resistance to Bremia lactucae, the casual fungus of downy mildew. Using a rapid and reliable screen, we identified 16 distinct mutants of Latuca sativa that have lost activity of one of four different downy mildew resistance genes (Dm). In all mutants, only a single Dm specificity was affected. Genetic analysis indicated that the lesions segregated as single, recessive mutations at the Dm loci. Dm3 was inactivated in nine of the mutants. One of five Dm 1 mutants was selected from a population of untreated seeds and therefore carried a spontaneous mutation. All other Dm1, Dm3, Dm5/8 and Dm7 mutants were derived from gamma- or fast neutron-irradiated seed. In two separate Dm 1 mutants and in each of the eight Dm3 mutants analyzed, at least one closely linked molecular marker was absent. Also, high molecular weight genomic DNA fragments that hybridized to a tightly linked molecular marker in wild type were either missing entirely or were truncated in two of the Dm3 mutants, providing additional evidence that deletions had occurred in these mutants. Absence of mutations at loci epistatic to the Dm genes suggested that such loci were either members of multigene families, were critical for plant survival, or encoded components of duplicated pathways for resistance; alternatively, the genes determining downy mildew resistance might be limited to the Dm loci.

scholarly journals Genetics of disease resistance in Arabidopsis to crop pathogens

2002 ◽  
Vol 38 (SI 1 - 6th Conf EFPP 2002) ◽  
pp. S151-S154 ◽  
Author(s):  
E.B. Holub ◽  
M. Tör ◽  
A. Cooper ◽  
P. Gordon ◽  
N. Gunn
Keyword(s):  
Disease Resistance ◽  
Disease Susceptibility ◽  
Molecular Genetic ◽  
Species Level ◽  
Null Mutation ◽  
R Genes ◽  
Structural Class ◽  
Albugo Candida ◽  
Hyaloperonospora Parasitica ◽  
Durable Disease Resistance

Arabidopsis is universally resistant as a species to many crop pathogens, including examples from other crucifers such<br />as Albugo candida and Hyaloperonospora parasitica from Brassica oleracea. This species level trait could potentially<br />provide a source of durable disease resistance in crops if examples can be found which are amenable to molecular genetic<br />characterization. Our research has developed from the observation that null mutation in Arabidopsis of a defense regulatory<br />gene EDS1 (enhanced disease susceptibility) is susceptible to isolates of A. candida and H. parasitica from brassica.<br />EDS1 is required by a major structural class of R-genes to confer resistance in Arabidopsis. We have therefore focused<br />on identifying R-genes in Arabidopsis that are responsible for conferring resistance to brassica pathogens.

scholarly journals Specific In Planta Recognition of Two GKLR Proteins of the Downy Mildew Bremia lactucae Revealed in a Large Effector Screen in Lettuce

2013 ◽  
Vol 26 (11) ◽  
pp. 1259-1270 ◽  
Author(s):  
Joost H. M. Stassen ◽  
Erik den Boer ◽  
Pim W. J. Vergeer ◽  
Annemiek Andel ◽  
Ursula Ellendorff ◽  
...  
Keyword(s):  
Immune Responses ◽  
Downy Mildew ◽  
Hypersensitive Response ◽  
Effector Proteins ◽  
Chromosome 9 ◽  
Downy Mildew Resistance ◽  
Chromosome 2 ◽  
Bremia Lactucae ◽  
In Planta ◽  
Effector Triggered Immunity

Breeding lettuce (Lactuca sativa) for resistance to the downy mildew pathogen Bremia lactucae is mainly achieved by introgression of dominant downy mildew resistance (Dm) genes. New Bremia races quickly render Dm genes ineffective, possibly by mutation of recognized host-translocated effectors or by suppression of effector-triggered immunity. We have previously identified 34 potential RXLR(-like) effector proteins of B. lactucae that were here tested for specific recognition within a collection of 129 B. lactucae-resistant Lactuca lines. Two effectors triggered a hypersensitive response: BLG01 in 52 lines, predominantly L. saligna, and BLG03 in two L. sativa lines containing Dm2 resistance. The N-terminal sequences of BLG01 and BLG03, containing the signal peptide and GKLR variant of the RXLR translocation motif, are not required for in planta recognition but function in effector delivery. The locus responsible for BLG01 recognition maps to the bottom of lettuce chromosome 9, whereas recognition of BLG03 maps in the RGC2 cluster on chromosome 2. Lactuca lines that recognize the BLG effectors are not resistant to Bremia isolate Bl:24 that expresses both BLG genes, suggesting that Bl:24 can suppress the triggered immune responses. In contrast, lettuce segregants displaying Dm2-mediated resistance to Bremia isolate Bl:5 are responsive to BLG03, suggesting that BLG03 is a candidate Avr2 protein.

scholarly journals The Arabidopsis TIR-NB-LRR Gene RAC1 Confers Resistance to Albugo candida (White Rust) and Is Dependent on EDS1 but not PAD4

2004 ◽  
Vol 17 (7) ◽  
pp. 711-719 ◽  
Author(s):  
Mohammad H. Borhan ◽  
Eric B. Holub ◽  
Jim L. Beynon ◽  
Kevin Rozwadowski ◽  
S. Roger Rimmer
Keyword(s):  
Positional Cloning ◽  
Rust Resistance ◽  
Interleukin 1 ◽  
Dominant Gene ◽  
Leucine Rich Repeat ◽  
Albugo Candida ◽  
White Rust ◽  
Candida Isolate ◽  
Turn Structure ◽  
Lrr Domain

Resistance to Albugo candida isolate Acem1 is conferred by a dominant gene, RAC1, in accession Ksk-1 of Arabidopsis thaliana. This gene was isolated by positional cloning and is a member of the Drosophila toll and mammalian interleukin-1 receptor (TIR) nucleotide-binding site leucine-rich repeat (NB-LRR) class of plant resistance genes. Strong identity of the TIR and NB domains was observed between the predicted proteins encoded by the Ksk-1 allele and the allele from an Acem1-susceptible accession Columbia (Col) (99 and 98%, respectively). However, major differences between the two predicted proteins occur within the LRR domain and mainly are confined to the β-strand/β-turn structure of the LRR. Both proteins contain 14 imperfect repeats. RAC1-mediated resistance was analyzed further using mutations in defense regulation, including: pad4-1, eds1-1, and NahG, in the presence of the RAC1 allele from Ksk-1. White rust resistance was completely abolished by eds1-1 but was not affected by either pad4-1 or NahG.

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