Unravelling R gene‐mediated disease resistance pathways in Arabidopsis

Abstract

Molecular genetic approaches were adopted in the model crucifer, Arabidopsis thaliana, to unravel components of RPP5- and RPP1-mediated disease resistance to the oomycete pathogen, Peronospora parasitica. The products of RPP5 and three genes comprising the RPP1 complex locus belong to a major subclass of nucleotide-binding/leucine-rich repeat (NB-LRR) resistance (R) protein that has amino-terminal homology to the cytoplasmic domains of Drosophila and mammalian Toll and interleukin-1 family receptors (the so called 'TIR' domain). Similarities in the domain architecture of these proteins and animal regulators of programmed cell death have also been observed. Mutational screens revealed a number of genes that are required for RPP5-conditioned resistance. Among these are EDS1 and PAD4. Both EDS1 and PAD4 precede the function of salicylic acid-mediated plant responses. The EDS1 and PAD4 genes were cloned and found to encode proteins with similarity to the catalytic site of eukaryotic lipases, suggesting that they may function by hydrolysing a lipid-based substrate.

Arabidopsis RAR1 Exerts Rate-Limiting Control of R Gene–Mediated Defenses against Multiple Pathogens

“…In plants, the ubiquitilation of proteins as a means of cellular regulation is poorly understood. However, a molecular connection was established recently between an Arabidopsis SCF complex containing the F box component TIR1 and regulated protein degradation in response to the phytohormone auxin (Gray et al, 2001).We found that the rpr1 mutations identified in our RPP5 suppressor screens (Parker et al, 2000) are defective alleles of SGT1b, one of two highly homologous SGT1 genes in Arabidopsis, suggesting another link between resistance signaling and ubiquitilation of proteins (Austin et al, 2002). SGT1b also is required for RPP7 resistance in Col-0 to Peronospora isolate Hiks1 (Tör et al, 2002).…”

“…Some Avr proteins are virulence factors that facilitate pathogen growth or interfere with basal plant defenses (Nimchuk et al, 2000;Staskawicz et al, 2001). R-Avr protein recognition commonly involves localized programmed plant cell death (the hypersensitive response [HR]), an oxidative burst producing reactive oxygen intermediates (ROI), and the accumulation of salicylic acid (SA), a phenolic molecule necessary for the induction of systemic immunity (systemic acquired resistance) (Feys and Parker, 2000).Plant R proteins share a limited repertoire of motifs with animal proteins that control innate immunity (Staskawicz et al, 2001). The most prevalent R gene class encodes predicted cytosolic proteins with a central nucleotide binding (NB) domain and C-terminal Leu-rich repeats (LRRs) (Dangl and Jones, 2001).…”

VASCULAR ASSOCIATED DEATH1, a Novel GRAM Domain–Containing Protein, Is a Regulator of Cell Death and Defense Responses in Vascular Tissues

“…Arabidopsis R (resistance) genes have been cloned that confer specific recognition to bacterial, viral, and fungal pathogens (Parker et al, 2000). After this recognition event, plant defense is regulated through a complex network of transduction pathways involving several signaling molecules: reactive oxygen species, nitric oxide, salicylic acid (SA), jasmonic acid (JA), and ethylene (Kunkel and Brooks, 2002).…”

The Role ofNDR1in Avirulence Gene-Directed Signaling and Control of Programmed Cell Death in Arabidopsis

“…Plants resist infection only if the pathogen carries a specific avirulence (avr) gene that is the matched cognate of one of these plant R genes. Mutant plants with nonfunctional alleles of a particular R gene fail to recognize a pathogen carrying the corresponding avr gene, and disease ensues (Parker et al, 2000;Staskawicz, 2001). With bacterial pathogens, this specificity of molecular recognition in at least some cases is associated with direct binding of the plant R gene product to the bacterial avr gene product (Scofield et al, 1996; Tang et al, 1996).…”