Salicylic acid inhibits gibberellin signaling through receptor interactions

It is well known that plants activate defense responses at the cost of growth. However, the underlying molecular mechanisms are not well understood. The phytohormones salicylic acid (SA) and gibberellin (GA) promote defense response and growth, respectively. Here we show that SA inhibits GA signaling to repress plant growth. We found that the SA receptor NPR1 interacts with the GA receptor GID1. Further biochemical studies revealed that NPR1 functions as an adaptor of ubiquitin E3 ligase to promote the polyubiquitination and degradation of GID1, which enhances the stability of DELLA proteins, the negative regulators of GA signaling. Genetic analysis suggested that NPR1, GID1, and DELLA proteins are all required for the SA-mediated growth inhibition. Collectively, our study not only uncovers a novel regulatory mechanism of growth–defense trade-off but also reveals the interaction of hormone receptors as a new mode of hormonal crosstalk.