Balanced plant helper NLR activation by a modified host protein complex.

Area of Science:

• Plant immunity
• Molecular biology
• Structural biology

Background:

• Nucleotide-binding leucine-rich repeat (NLR) receptors are key regulators of plant immunity, detecting pathogen effectors.
• Sensor NLRs in Arabidopsis act as NADases, producing second messengers that trigger immune signaling.
• The enhanced disease susceptibility 1 (EDS1)-senescence-associated gene 101 (SAG101) complex recognizes these second messengers to activate downstream components.

Purpose of the Study:

• To elucidate the structural basis of NRG1A activation by the EDS1-SAG101 complex.
• To understand the mechanism by which NRG1C inhibits the plant immune response.
• To reveal the molecular interplay governing the activation and constraint of a central plant immune pathway.

Main Methods:

• Cryoelectron microscopy (cryo-EM) to determine the structure of the EDS1-SAG101-NRG1A complex.
• Structural comparisons to identify conformational changes upon second messenger binding.
• Biochemical assays to assess the binding interactions between EDS1-SAG101, NRG1A, and NRG1C.

Main Results:

• Cryo-EM revealed that activated EDS1-SAG101 binds the leucine-rich repeat domain of NRG1A, forming a stable complex.
• Second messenger binding induces conformational changes in EDS1-SAG101, which are recognized by NRG1A, leading to its allosteric activation.
• The inhibitory NRG1C protein competes with NRG1A for binding to activated EDS1-SAG101, effectively sequestering the complex.

Conclusions:

• The study uncovers the mechanism of NRG1A activation via recognition of a modified EDS1-SAG101 complex.
• NRG1C inhibits the immune response by preventing NRG1A activation through competitive binding to EDS1-SAG101.
• These findings provide critical insights into the regulation of plant immune signaling pathways.