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Updated: Jun 12, 2026
Avidity-based Extracellular Interaction Screening (AVEXIS) for the Scalable Detection of Low-affinity Extracellular Receptor-Ligand Interactions
Published on: March 5, 2012
ER retrieval of Avr9 compromises its elicitor activity consistent with perception of Avr9 at the plasma membrane
Ryan J Wilson1, Brett K Baillie, David A Jones
1Research School of Biological Sciences, The Australian National University, Canberra, ACT 0200, Australia.
Abstract:
SUMMARY The discovery of an endoplasmic reticulum (ER) retrieval motif at the C-terminus of the predicted Cf-9 resistance protein suggested that Cf-9 might function in the ER. To test whether Cf-9 could detect its cognate avirulence protein, Avr9, from the ER, variants of Avr9 with the ER retrieval motifs KDEL or HDEL were transiently expressed in Cf-9 tobacco. Cf-9-mediated necrosis in response to Avr9 tagged at the C-terminus with the KDEL motif was substantially delayed compared with unmodified Avr9. Interestingly, necrosis was completely abolished when Avr9 was tagged with the HDEL motif. Introduction of the S5A mutation, which destroys the sole N-linked glycosylation site of Avr9, ruled out the possibility that an ER-specific pattern of glycosylation prevented a response to the KDEL or HDEL variants of Avr9. These results suggest that Avr9 is perceived at the plasma membrane. They also suggest that HDEL is a more effective ER retrieval motif than KDEL in tobacco.
Insights
The Cf-9 resistance protein likely recognizes Avr9 at the plasma membrane, not the endoplasmic reticulum (ER). Tagging Avr9 with ER retrieval motifs (KDEL/HDEL) altered or abolished the plant
Area of Science:
- Plant pathology
- Molecular biology
- Plant-pathogen interactions
Background:
- The Cf-9 resistance protein contains a C-terminal endoplasmic reticulum (ER) retrieval motif, suggesting a potential ER localization and function.
- The interaction between plant resistance proteins and pathogen avirulence proteins is crucial for plant immunity.
Purpose of the Study:
- To investigate the cellular localization where the Cf-9 resistance protein recognizes its cognate avirulence protein, Avr9.
- To determine if Avr9 can be detected by Cf-9 from within the ER.
Main Methods:
- Transient expression of Avr9 variants, engineered with ER retrieval motifs (KDEL or HDEL), in Cf-9 transgenic tobacco plants.
- Analysis of Cf-9-mediated necrosis as a response to Avr9 variants.
- Introduction of an S5A mutation to disrupt the Avr9 N-linked glycosylation site.
Main Results:
- Cf-9-mediated necrosis was delayed when Avr9 was tagged with the KDEL motif compared to unmodified Avr9.
- Necrosis was completely abolished when Avr9 was tagged with the HDEL motif.
- Glycosylation status did not account for the altered responses to KDEL- and HDEL-tagged Avr9.
Conclusions:
- The results suggest that Avr9 is perceived by Cf-9 at the plasma membrane, not within the ER.
- HDEL appears to be a more potent ER retrieval signal than KDEL in tobacco.
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