Two TIR:NB:LRR genes are required to specify resistance to Peronospora parasitica isolate Cala2 in Arabidopsis

Abstract

These authors made an equal contribution to the work reported. SummaryResistance responses that plants deploy in defence against pathogens are often triggered following a recognition event mediated by resistance (R) genes. The encoded R proteins usually contain a nucleotide-binding site (NB) and a leucine-rich repeat (LRR) domain. They are further classi®ed into those that contain an N-terminal coiled coil (CC) motif or a Toll interleukin receptor (TIR) domain. Such R genes, when transferred into a susceptible plant of the same or closely related species, usually impart full resistance capability. We have used map-based cloning and mutation analysis to study the recognition of Peronospora parasitica (RPP)2 (At) locus in Arabidopsis accession Columbia (Col-0), which is a determinant of speci®c recognition of P. parasitica (At) isolate Cala2. Genetic mapping located RPP2 to a 200-kb interval on chromosome 4, which contained four adjacent TIR:NB:LRR genes. Mutational analysis revealed three classes of genes involved in specifying resistance to Cala2. One class, which resulted in pleiotropic effects on resistance to other P. parasitica (At) isolates, was unlinked to the RPP2 locus; this class included AtSGT1b. The other two classes were mapped within the interval and were speci®c to Cala2 resistance. Representatives of each of these classes were sequenced, and mutations were found in one or the other of two (RPP2A and RPP2B) of the four TIR:NB:LRR genes. RPP2A and RPP2B complemented their speci®c mutations, but failed to impart resistance when present alone, and it is concluded that both genes are essential determinants for isolate-speci®c recognition of Cala2. RPP2A has an unusual structure with a short LRR domain at the Cterminus, preceded by two potential but incomplete TIR:NB domains. In addition, the RPP2A LRR domain lacks conserved motifs found in all but three other TIR:NB:LRR class proteins. In contrast, RPP2B has a complete TIR:NB:LRR structure. It is concluded that RPP2A and RPP2B cooperate to specify Cala2 resistance by providing recognition or signalling functions lacked by either partner protein.

Two Adjacent Nucleotide-Binding Site–Leucine-Rich Repeat Class Genes Are Required to Confer Pikm-Specific Rice Blast Resistance

“…ple is the gene RPP2 in Arabidopsis (Sinapidou et al 2004). Resistance to Cala2, specified by the RPP2 locus in Arabidopsis Col-0, requires two genes, RPP2A and RPP2B, both of which reside at the RPP2 locus and are NBS-LRR-class genes.…”

Downy Mildew Resistance in Arabidopsis by Mutation of HOMOSERINE KINASE

“…The dmr1 mutants were backcrossed twice (BC 2 ), to reduce the number of unlinked EMS-induced mutations, to the parental line Ler eds1-2 and to Ler containing the wild-type EDS1 gene. A mapping population was generated by crossing the mutant to Columbia-0 (Col-0) FN2 (Sinapidou et al, 2004), and the resistant F2 plants were selected, genotyped, and rescreened for resistance in the F3. The dmr1 phenotype was found to be linked to the ciw3 and nga1126 markers (www.arabidopsis.org) on chromosome 2.…”

Differential Recognition of Highly Divergent Downy Mildew Avirulence Gene Alleles by RPP1 Resistance Genes from Two Arabidopsis Lines

“…RPP proteins perceive avirulence (Arabidopsis thaliana Recognized [ATR]) gene products produced by H. parasitica isolates and trigger resistance responses. Coevolving populations of Arabidopsis and H. parasitica have been used to genetically define and clone Arabidopsis RPP genes that represent two intracellular classes and an extracellular class of Leu-rich repeat disease resistance genes (Holub et al, 1994;Parker et al, 1997;Botella et al, 1998;McDowell et al, 1998;Bittner-Eddy et al, 2000;van der Biezen et al, 2002;Sinapidou et al, 2004;Tö r et al, 2004). Studying the interaction between RPP proteins and their H. parasitica targets represents an opportunity to examine the mechanisms underlying host resistance to, and parasite pathogenicity of, a naturally occurring parasite of the model plant Arabidopsis.…”