Two putative BIN2 substrates are nuclear components of brassinosteroid signaling

Jun Zhao, Peng Peng, Robert J. Schmitz, Adria D. Decker, Frans E. Tax, Jianming Li

Research output: Contribution to journalArticle

133 Scopus citations

Abstract

GSK3 is a highly conserved kinase that negatively regulates many cellular processes by phosphorylating a variety of protein substrates. BIN2 is a GSK3-like kinase in Arabidopsis that functions as a negative regulator of brassinosteroid (BR) signaling. It was proposed that BR signals, perceived by a membrane BR receptor complex that contains the leucine (Leu)-rich repeat receptor-like kinase BRI1, inactivate BIN2 to relieve its inhibitory effect on unknown downstream BR-signaling components. Using a yeast (Saccharomyces cerevisiae) two-hybrid approach, we discovered a potential BIN2 substrate that is identical to a recently identified BR-signaling protein, BES1. BES1 and its closest homolog, BZR1, which was also uncovered as a potential BR-signaling protein, display specific interactions with BIN2 in yeast. Both BES1 and BZR1 contain many copies of a conserved GSK3 phosphorylation site and can be phosphorylated by BIN2 in vitro via a novel GSK3 phosphorylation mechanism that is independent of a priming phosphorylation ora scaffold protein. Five independent bes1 alleles containing the same proline-233-Leu mutation were identified as semidominant suppressors of two different bri1 mutations. Overexpression of the wild-type BZR1 gene partially complemented bin2/+ mutants and resulted in a BRI1 overexpression phenotype in a BIN2+ background, whereas overexpression of a mutated BZR1 gene containing the corresponding proline-234-Leu mutation rescued a weak bri1 mutation and led to a bes1-like phenotype. Confocal microscopic analysis indicated that both BES1 and BZR1 proteins were mainly localized in the nucleus. We propose that BES1/BZR1 are two nuclear components of BR signaling that are negatively regulated by BIN2 through a phosphorylation-initiated process.

Original languageEnglish (US)
Pages (from-to)1221-1229
Number of pages9
JournalPlant physiology
Volume130
Issue number3
DOIs
StatePublished - Nov 1 2002
Externally publishedYes

ASJC Scopus subject areas

  • Physiology
  • Genetics
  • Plant Science

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