Estradiol-inducible AvrRps4 expression reveals distinct properties of TIR-NLR-mediated effector-triggered immunity

Abstract

Plant nucleotide-binding domain, leucine-rich repeat receptor (NLR) proteins play important roles in recognition of pathogen-derived effectors. However, the mechanism by which plant NLRs activate immunity is still largely unknown. The paired Arabidopsis NLRs RRS1-R and RPS4, that confer recognition of bacterial effectors AvrRps4 and PopP2, are well studied, but how the RRS1/RPS4 complex activates early immediate downstream responses upon effector detection is still poorly understood. To study RRS1/RPS4 responses without the influence of cell-surface receptor immune pathways, we generated an Arabidopsis line with inducible expression of effector AvrRps4. Induction does not lead to hypersensitive cell death response (HR) but can induce electrolyte leakage, which often correlates with plant cell death. Activation of RRS1 and RPS4 without pathogens cannot activate mitogen-associated protein kinase cascades, but still activates upregulation of defense genes, and therefore resistance against bacteria.HighlightInducible expression of AvrRps4 activates RRS1/RPS4-mediated effector-triggered immunity without the presence of pathogens, allowing us to characterise downstream immune responses triggered by TIR-NLRs without cell-surface receptor-mediated immunity.

Chromatin accessibility landscapes activated by cell-surface and intracellular immune receptors

“…Arabidopsis thaliana Columbia-0 (Col-0) accession was used as wild type in this study. SETI WT and SETI mut transgenic plants used have been described previously (Ngou et al, 2020b). Seeds were sown on compost and plants were grown at 21 °C with 10 hours under light and 14 hours in dark, and at 70% humidity.…”

“…Activation of ETI. 5-week-old Arabidopsis leaves of SETI WT (E2:AvrRps4 WT ) infiltrated with 50 µM βestradiol (E2, Sigma-Aldrich, catalogue number: E8875; dissolved in 100% dimethyl sulfoxide, also known as DMSO, Sigma-Aldrich, catalogue number: D8418) activates 'ETI' only, as described previously (Ngou et al, 2020b). 0.1% DMSO (same titrate as 50 mM E2 stock solution diluted in pure water and generating 50 µM E2 working solution) in pure water used as mock treatment for infiltration with a 1-mL needleless syringe.…”

“…This implies that ETI-enhanced transcriptional regulation plays an essential role in conferring robust immune responses against pathogens (Ngou et al, 2020a), but how ETI activates defense genes remains unclear. To study ETI-specific physiological changes, we generated an inducible ETI system (Ngou et al, 2020b).…”

Mutual Potentiation of Plant Immunity by Cell-surface and Intracellular Receptors

“…When 35 Arabidopsis is infiltrated with a non-pathogenic strain P. fluorescens Pf0-1 delivering wild-type AvrRps4 (Pf0-1:AvrRps4 WT ), which triggers "PTI + ETI AvrRps4 ", cell death is observed (Extended Data Fig 6A). However, ETI AvrRps4 alone does not lead to HR (Extended Data Fig 6A) 12 . To explain this discrepancy, we hypothesized that co-activation of PTI is required for ETI AvrRps4 to induce HR.…”

“…Pre-activation of ETI AvrRps4 10 elevates plant resistance against virulent bacteria Pseudomonas syringae pv. tomato (Pst) DC3000 12 . We tested if this enhanced resistance is due to potentiation of PTI responses by ETI AvrRps4 .…”