Abstract
Specificity in the plant immune system is mediated by Resistance (R) proteins. Most R genes encode intracellular NLR-type immune receptors and these pathogen sensors require helper NLRs to activate immune signaling upon pathogen perception. Resistance conferred by many R genes is temperature sensitive and compromised above 28°C. Many Solanaceae R genes, including the potato NLR Rx1 conferring resistance to Potato Virus X (PVX), have been reported to be temperature labile. Rx1 activity, like many Solanaceae NLRs, depends on helper-NLRs called NRC’s. In this study, we investigated Rx1 resistance at elevated temperatures in potato and in Nicotiana benthamiana plants stably expressing Rx1 upon rub-inoculation with GFP-expressing PVX particles. In parallel, we used susceptible plants as a control to assess infectiousness of PVX at a range of different temperatures. Surprisingly, we found that Rx1 confers virus resistance in N. benthamiana up to 32°C, a temperature at which the PVX::GFP lost infectiousness. Furthermore, at 34°C, an Rx1-mediated hypersensitive response could still be triggered in N. benthamiana upon PVX Coat-Protein overexpression. As the Rx1-immune signaling pathway is not temperature compromised, this implies that at least one N. benthamiana helper NRC and its downstream signaling components are temperature tolerant. This finding suggests that the temperature sensitivity for Solanaceous resistances is likely attributable to the sensor NLR and not to its downstream signaling components.
Highlights
Plants have developed a multi-layered immune system activated by receptor proteins that detect pathogen-generated molecules
As no viral RNAs were detected at 32◦C or above in Rx1 plants, this suggests that Rx1 is able to confer resistance to Potato Virus X (PVX)::GFP in N. benthamiana at least up to temperatures at which the virus is no longer infectious
We show that Rx1-mediated resistance to PVX::GFP in N. benthamiana remains functional up to a temperature at which the virus was no longer infectious
Summary
Plants have developed a multi-layered immune system activated by receptor proteins that detect pathogen-generated molecules. Immune receptors can be classified into two main groups: (i) the extracellular receptors, mainly Receptor like-Kinases (RLK) or -Proteins (RLP), commonly associated with either recognition of pathogens’ conserved features (microbial- or pathogen associated molecular patterns, MAMP or PAMP) or by pathogen inflicted damage (damage associated molecular patterns or DAMP) and (ii) Intracellular receptors. Members of this latter group often encode Nucleotide-binding domain and leucine-rich repeat (NLR) proteins that recognize specific pathogen encoded avirulence factors (Avr) (Dodds and Rathjen, 2010). NLR activation often triggers local cell death, the so-called hypersensitive response (HR) (Balint-Kurti, 2019)
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