Proteolysis of the barley receptor-like protein kinase RPG1 by a proteasome pathway is correlated with Rpg1 -mediated stem rust resistance

Abstract

In plants, disease resistance mediated by the gene-for-gene mechanism involves the recognition of specific effector molecules produced by the pathogen either directly or indirectly by the resistance-gene products. This recognition triggers a series of signals, thereby serving as a molecular switch in regulating defense mechanisms by the plants. To understand the mechanism of action of the barley stem rust resistance gene Rpg1, we investigated the fate of the RPG1 protein in response to infection with the stem rust fungus, Puccinia graminis f. sp. tritici. The investigations revealed that RPG1 disappears to undetectable limits only in the infected tissues in response to avirulent, but not virulent pathotypes. The RPG1 protein disappearance is rapid and appears to be due to specific protein degradation via the proteasome-mediated pathway as indicated by inhibition with the proteasomal inhibitor MG132, but not by other protease inhibitors.avirulence ͉ cultivar ͉ programmed cell death ͉ Puccinia graminis P lants have evolved diverse mechanisms to recognize pathogen attack and trigger defense responses. Pathogen recognition specificity is often determined by a pathogen avirulence (Avr) gene and its corresponding plant resistance (R) gene in a gene for gene manner (1). The R gene products may function directly or indirectly as receptors for the Avr gene products, providing detection of pathogen attack (2-6). Avr proteins secreted from the pathogen are recognized by the R proteins either in the intercellular spaces or after their transport into the plant cell. The Avr-R interactions lead to activation of defense responses and often result in the hypersensitive response (HR) (1), inhibiting the growth of the pathogen. In the absence of either the cognate R or Avr gene product, the pathogen colonizes the host and causes disease. Despite the cloning of several R genes and their corresponding Avr genes, direct physical interaction between matched Avr and R proteins has been shown only in a few cases. To exemplify, the Avr-Pita protein of the rice blast fungus Magnaporthe grisea encoding a metalloprotease is secreted with an N-terminal signal sequence. After delivery into the plant cell and removal of the proprotein sequence, the mature enzyme binds to the leucine-rich domain of the Pi-ta R protein and elicits the resistance response. This interaction was confirmed with the yeast two-hybrid system, with transient expression in rice seedling leaves of resistant or susceptible lines, by in vitro binding of the recombinantly synthesized Pi-ta protein to the Avr-Pita protein and by inactivation of either of the proteins through amino acid substitutions (7). Direct physical interaction has been demonstrated for the tomato Pto R protein and the AvrPto gene product (2, 4), the Arabidopsis RRS1 R and Ralstonia solanacearum PopP2 (8), and between the flax R gene L6 with the corresponding Avr-L6 of Melampsora lini (9). However, attempts with other R-Avr pairs have failed to establish a direct physical interaction. These observations ...

Plant Innate Immunity: Perception of Conserved Microbial Signatures

“…RPG1 localizes to the plasma membrane and cytosol, where it is phosphorylated within minutes after urediniospore attachment to the leaf surface (154). Phosphorylation is required for RPG1 protein degradation via the proteasome pathway after pathogen perception, and both kinases are required for disease resistance (153,154).…”

The Wheat Mitogen-Activated Protein Kinases TaMPK3 and TaMPK6 Are Differentially Regulated at Multiple Levels during Compatible Disease Interactions withMycosphaerella graminicola

“…Precedent exists for the selective degradation of plant signaling proteins during pathogen attack. For example, studies on the interaction of barley (Hordeum vulgare) with the biotrophic stem rust fungus identified a specific proteolysis of the RPG1 receptor-like kinase that preceded the execution of HR-mediated disease resistance responses (Nirmala et al, 2007). During our time course studies, there was Figure 8.…”

Concerted action of two avirulent spore effectors activates Reaction to Puccinia graminis 1 ( Rpg1 ) - mediated cereal stem rust resistance

“…Rpg1 is constitutively expressed (39) and is mostly cytoplasmic, with a small fraction associated with the plasma membrane (38). On inoculation with stem rust urediniospores, RPG1 is phosphorylated in vivo within 5 min (40) and is subsequently degraded (41). Both actions are required for resistance.…”