Nucleotide-binding domain and leucine-rich repeat domain-containing (NLR) proteins are sentinels of plant immunity that monitor host proteins for perturbations induced by pathogenic effector proteins. Here we show that the Arabidopsis ZAR1 NLR protein requires the ZRK3 kinase to recognize the Pseudomonas syringae type III effector (T3E) HopF2a. These results support the hypothesis that ZAR1 associates with an expanded ZRK protein family to broaden its effector recognition spectrum.

The cell wall is a complex polysaccharide network that provides stability and protection to the plant and is one of the first layers of biotic and abiotic stimuli perception. A controlled remodeling of the primary cell wall is essential for the plant to adapt its growth to environmental stresses. Cellulose, the main component of plant cell walls is synthesized by plasma membrane-localized cellulose synthases moving along cortical microtubule tracks. Recent advancements demonstrate a tight regulation of cellulose synthesis at the primary cell wall by phytohormone networks. Stress-induced perturbations at the cell wall that modify cellulose synthesis and microtubule arrangement activate similar phytohormone-based stress response pathways. The integration of stress perception at the primary cell wall and downstream responses are likely to be tightly regulated by phytohormone signaling pathways in the context of cellulose synthesis and microtubule arrangement.

Environmental adaptation of organisms relies on fast perception and response to external signals, which lead to developmental changes. Plant cell growth is strongly dependent on cell wall remodeling. However, little is known about cell wall‐related sensing of biotic stimuli and the downstream mechanisms that coordinate growth and defense responses. We generated genetically encoded pH sensors to determine absolute pH changes across the plasma membrane in response to biotic stress. A rapid apoplastic acidification by phosphorylation‐based proton pump activation in response to the fungus Fusarium oxysporum immediately reduced cellulose synthesis and cell growth and, furthermore, had a direct influence on the pathogenicity of the fungus. In addition, pH seems to influence cellulose structure. All these effects were dependent on the COMPANION OF CELLULOSE SYNTHASE proteins that are thus at the nexus of plant growth and defense. Hence, our discoveries show a remarkable connection between plant biomass production, immunity, and pH control, and advance our ability to investigate the plant growth‐defense balance.

Pseudomonas syringae is a Gram-negative bacterium that infects multiple plant species by manipulating cellular processes via injection of type three secreted effectors (T3SEs) into host cells. Nucleotide-binding leucine-rich repeat (NLR) resistance (R) proteins recognize specific T3SEs and trigger a robust immune response, called effector-triggered immunity (ETI), which limits pathogen proliferation and is often associated with localized programmed cell death, known as the hypersensitive response (HR). In this study, we examine the influence of elevated temperature on two ETI outputs: HR and pathogen virulence suppression. We found that in the Arabidopsis thaliana accession Col-0, elevated temperatures suppress the HR, but have minimal influence on ETI-associated P. syringae virulence suppression, thereby uncoupling these two ETI responses. We also identify accessions of Arabidopsis that exhibit impaired P. syringae virulence suppression at elevated temperature, highlighting the natural variation that exists in coping with biotic and abiotic stresses. These results not only reinforce the influence of abiotic factors on plant immunity but also emphasize the importance of carefully documented environmental conditions in studies of plant immunity.

Environmental adaptation of organisms relies on fast perception and response to external signals, which lead to developmental changes. Plant cell growth is strongly dependent on cell wall remodeling. However, little is known about cell wall-related sensing of biotic stimuli and the downstream mechanisms that coordinate growth and defense responses. We generated genetically encoded pH sensors to determine absolute pH changes across the plasma membrane in response to biotic stress. A rapid apoplastic acidification by phosphorylation-based proton pump activation was followed by an acidification of the cortical side of the plasma membrane in response to the fungus Fusarium oxysporum. The proton chemical gradient modulation immediately reduced cellulose synthesis and cell growth and, furthermore, had a direct influence on the pathogenicity of the fungus. All these effects were dependent on the COMPANION OF CELLULOSE SYNTHASE proteins that are thus at the nexus of plant growth and defense. Hence, our discoveries show a remarkable connection between plant biomass production, immunity, and pH control, and advance our ability to investigate the plant growth-defense balance. We are grateful to G. Sancho-Andrés, B. Pfister, and P. van Dam for technical support. We thank S. Persson for the cc1cc2 , cc1cc2 GFP-CC1 and cc1cc2 GFP-CC1ΔN120 lines and A. Molina, G. Bissoli and E. López-Solanilla for constructive discussions. Live cell imaging was performed with equipment maintained by