Characterization of SBZ1, a soybean bZIP protein that binds to the chalcone synthase gene promoter

摘要

Several plant basic leucine zipper (bZIP) proteins have been shown to play a role in chalcone synthase (CHS) gene expression, and some are regulated by phosphorylation/dephosphorylation. We isolated SBZ1 (Soybean bZIP protein 1) and showed that the recombinant protein binds in vitro to the 5' region of soybean CHS1, at a sequence that confers the elicitor-inducible expression of CHS genes. The deduced amino acid sequence of SBZ1 has features characteristic of bZIP transcription factors, including a highly basic putative DNA-binding domain containing a nuclear localization sequence, as well as four domains designated D1-D4 that are highly conserved among the subfamily of bZIP factors, which includes tobacco BZI-1 and parsley CPRF2. The presence of these regions indicates that SBZ1 is a CPRF2-related bZIP transcription factor. The protein kinase inhibitor K252a blocks CHS induction in elicited soybean cells, suggesting that protein phosphorylation is involved in induction of the CHS signal pathway. Phosphorylation assays indicated that SBZ1 is phosphorylated in vitro in a soybean cell extract, and that this phosphorylation depends on Ca-2 broken vertical bar. Furthermore, recombinant soybean CDPK and the a subunit of CKII phosphorylate SBZ1 in vitro. However, unlike other related bZIP proteins, phosphorylation had no effect on either the DNA-binding activity of SBZ1. Therefore, we conclude that SBZ1 is regulated by phosphorylation, but in a different manner than are related bZIP factors.