NADase and now Ca2+ channel, what else to learn about plant NLRs?

Activation and inhibition mechanisms of a plant helper NLR

Plant nucleotide-binding leucine-rich repeat (NLR) receptors sense pathogen effectors and form resistosomes to confer immunity1. Some sensor NLR resistosomes produce small molecules to induce formation of a heterotrimer complex with two lipase-like proteins, EDS1 and SAG101, and a helper NLR called NRG1 (refs. 2,3). Activation of sensor NLR resistosomes also triggers NRG1 oligomerization and resistosome formation at the plasma membrane4,5. We demonstrate that the Arabidopsis AtEDS1-AtSAG101-AtNRG1A heterotrimer formation is stabilized by the AtNRG1A loss-of-oligomerization mutant L134E5,6. We report structures of AtEDS1-AtSAG101-AtNRG1A L134E and AtEDS1-AtSAG101-AtNRG1C heterotrimers with similar assembly mechanisms. AtNRG1A signalling is activated by the interaction with the AtEDS1-AtSAG101 heterodimer in complex with their small-molecule ligand. The truncated AtNRG1C maintains core interacting domains of AtNRG1A but develops further interactions with AtEDS1-AtSAG101 to outcompete AtNRG1A. Moreover, AtNRG1C lacks an N-terminal signalling domain and shows nucleocytoplasmic localization, facilitating its sequestration of AtEDS1-AtSAG101, which is also nucleocytoplasmic. Our study shows the activation and inhibition mechanisms of a plant helper NLR.

Calcium channels and transporters: Roles in response to biotic and abiotic stresses

Calcium (Ca2+) serves as a ubiquitous second messenger by mediating various signaling pathways and responding to numerous environmental conditions in eukaryotes. Therefore, plant cells have developed complex mechanisms of Ca2+ communication across the membrane, receiving the message from their surroundings and transducing the information into cells and organelles. A wide range of biotic and abiotic stresses cause the increase in [Ca2+]cyt as a result of the Ca2+ influx permitted by membrane-localized Ca2+ permeable cation channels such as CYCLIC NUCLEOTIDE-GATE CHANNELs (CNGCs), and voltage-dependent HYPERPOLARIZATION-ACTIVATED CALCIUM2+ PERMEABLE CHANNELs (HACCs), as well as GLUTAMATE RECEPTOR-LIKE RECEPTORs (GLRs) and TWO-PORE CHANNELs (TPCs). Recently, resistosomes formed by some NUCLEOTIDE-BINDING LEUCINE-RICH REPEAT RECEPTORs (NLRs) are also proposed as a new type of Ca2+ permeable cation channels. On the contrary, some Ca2+ transporting membrane proteins, mainly Ca2+-ATPase and Ca2+/H+ exchangers, are involved in Ca2+ efflux for removal of the excessive [Ca2+]cyt in order to maintain the Ca2+ homeostasis in cells. The Ca2+ efflux mechanisms mediate the wide ranges of cellular activities responding to external and internal stimuli. In this review, we will summarize and discuss the recent discoveries of various membrane proteins involved in Ca2+ influx and efflux which play an essential role in fine-tuning the processing of information for plant responses to abiotic and biotic stresses.