The brassinosteroid receptor BRI 1 can generate cGMP enabling cGMP ‐dependent downstream signaling

Abstract

The brassinosteroid receptor brassinosteroid insensitive 1 (BRI 1) is a member of the leucine‐rich repeat receptor‐like kinase family. The intracellular kinase domain of BRI 1 is an active kinase and also encapsulates a guanylate cyclase catalytic centre. Using liquid chromatography tandem mass spectrometry, we confirmed that the recombinant cytoplasmic domain of BRI 1 generates pmol amounts of cGMP per μg protein with a preference for magnesium over manganese as a co‐factor. Importantly, a functional BRI 1 kinase is essential for optimal cGMP generation. Therefore, the guanylate cyclase activity of BRI 1 is modulated by the kinase while cGMP , the product of the guanylate cyclase, in turn inhibits BRI 1 kinase activity. Furthermore, we show using Arabidopsis root cell cultures that cGMP rapidly potentiates phosphorylation of the downstream substrate brassinosteroid signaling kinase 1 (BSK 1). Taken together, our results suggest that cGMP acts as a modulator that enhances downstream signaling while dampening signal generation from the receptor.