Phytohormone brassinosteroids (BRs) play important roles in regulating plant development. By manipulating level or sensitivity it can display crucial roles in regulating rice architecture, and it has the potential to improve rice yields. The components of BR signaling have been widely studied in Arabidopsis.

Membrane-located receptor BRI1 (BR Insensitive1, a receptor-like kinase) perceives BR signal, whose activity is stimulated by BR-induced BRI1-BAK1 (BRI1-Associated Kinase1) hetero-dimerization or negatively regulated by BRI1 internalization modification with ubiquitination. However, only a few components involved in rice BR signaling have been identified and the functional mechanism of BR in monocots needs further investigations.

Prof. XUE Hongwei and his colleagues at Shanghai Institute of Plant Physiology and Ecology of Chinese Academy of Sciences identify elt1-D, a gain-of-function rice mutant presenting reduced height and significantly increased tiller number and leaf inclination. The study was published in Cell Research.  

Genetic analysis showed that the elt1-D phenotype results from the enhanced BR signaling. Although being well conserved with enzymatically active serine/threonine kinases, the ELT1 intercellular domain does not present kinase activity. Further analysis revealed that tissue-specific ELT1 stimulates BR signaling by suppressing endocytosis-mediated degradation of BRI1 through interaction. 

The study identified ELT1 as a novel key component of BR signaling, and help to illustrate the molecular mechanism of BR functions in determining distinct agricultural traits of crops. It would facilitate functions and relevant mechanisms studies of RLKs which lack kinase activity in various physiological processes.

The study was supported by Ministry of Science and Technology of China, the Chinese Academy of Sciences, and the National Natural Science Foundation of China.