“Salicylic acid (SA) is a plant hormone that is critical for resistance to pathogens.”  So begins a pivotal new study by Xinnian Dong’s lab in collaboration with Ning Zheng’s lab at the University of Washington (“Structural basis of salicylic acid perception by Arabidopsis NPR proteins.” Nature 586, 311-316).  Plant pathologists have long known that the NPR proteins are responsible for sensing the presence of SA, but not how they do it.  Now Dong and Zheng et al. have unfolded the crystal structure of two different forms of NPR and demonstrated how they play opposite roles when interacting with SA.  NPR1 uses SA to activate the plant’s defenses, while NPR4 represses gene defense and is deactivated by SA to clear the way for response to the pathogen.  Using crystallography the two groups identified a pocket in the structure of NPR4 and showed how it binds to SA, conpletely enclosing the hormone.  This alters the configuration of the protein so that it can no longer interact with its partners to repress the genes needed for defense.

This was an immense project that required many different analytical techniques.  Congratulations to all for their individual roles and to the lab heads for coordinating the many different approaches.