A life or death switch

The identification of two receptors for salicylic acid reveals how the hormone controls cell death and survival during plant immune responses, in tissues close to and distant from the site of infection. See Letter p.228 Salicylic acid is the only major plant hormone for which a receptor has not been firmly identified. It is produced in plants in response to pathogen challenge, and induces systemic acquired resistance against secondary infection. This process requires the transcription cofactor NPR1, which indicated that NPR1 might be a salicylic acid receptor, but NPR1 alone does not bind to the hormone. Here, Xinnian Dong and colleagues identify the NPR1 paralogues NPR3 and NPR4 as salicylic acid receptors with different binding affinities. The authors propose a model for the regulation of NPR1 by NPR3 and NPR4 in response to different levels of salicylic acid.