ORIGINAL ARTICLE

Cell Research (2008): 472-478
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Is kinase activity essential for biological functions of BRI1?

Weihui Xu^1,*, Juan Huang^1,2,*, Baohua Li¹, Jiayang Li¹ and Yonghong Wang¹

Correspondence: Yonghong Wang Tel: +86 10 64836038; Fax: +86 10 64873428 E-mail: yhwang@genetics.ac.cn *These two authors contributed equally to this work.

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Brassinosteroids (BRs) are a major group of plant hormones that regulate plant growth and development. BRI1, a protein localized to the plasma membrane, functions as a BR receptor and it has been proposed that its kinase activity has an essential role in BR-regulated plant growth and development. Here we report the isolation and molecular characterization of a new allele of bri1, bri1-301, which shows moderate morphological phenotypes and a reduced response to BRs under normal growth conditions. Sequence analysis identified a two-base alteration from GG to AT, resulting in a conversion of 989G to 989I in the BRI1 kinase domain. An in vitro assay of kinase activity showed that bri1-301 has no detectable autophosphorylation activity or phosphorylation activity towards the BRI1 substrates TTL and BAK1. Furthermore, our results suggest that bri1-301, even with extremely impaired kinase activity, still retains partial function in regulating plant growth and development, which raises the question of whether BRI1 kinase activity is essential for BR-mediated growth and development in higher plants.

Cell Research (2008) 18:472–478. doi: 10.1038/cr.2008.36; published online 11 March 2008

Keywords: brassinosteroid, bri1, kinase activity, Arabidopsis thaliana