Two Putative BIN2 Substrates Are Nuclear Components of Brassinosteroid Signaling1
AUTOR(ES)
Zhao, Jun
FONTE
American Society of Plant Biologists
RESUMO
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 or a scaffold protein. Five independent bes1 alleles containing the same proline-233-Leu mutation were identified as semidominant suppressors of two different bri1 mutations. Over-expression 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.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=166643Documentos Relacionados
- The GSK3-like kinase BIN2 phosphorylates and destabilizes BZR1, a positive regulator of the brassinosteroid signaling pathway in Arabidopsis
- Brassinosteroid Mutants Uncover Fine Tuning of Phytochrome Signaling1
- The ULTRACURVATA2 Gene of Arabidopsis Encodes an FK506-Binding Protein Involved in Auxin and Brassinosteroid Signaling1
- BIN2, a New Brassinosteroid-Insensitive Locus in Arabidopsis1
- Endocytosis, Actin Cytoskeleton, and Signaling1