Characterization of SBZ1, a soybean bZIP protein that binds to the chalcone synthase gene promoter
Several plant basic leucine zipper (bZIP) proteins have been shown to play a role in chalcone synthase (<i>CHS</i>) gene expression, and some are regulated by phosphorylation/dephosphorylation. We isolated <i>SBZ1</i> (Soybean bZIP protein 1) and showed that the recombinant protein binds <i>in vitro</i> to the 5′ region of soybean <i>CHS1</i>, at a sequence that confers the elicitor-inducible expression of <i>CHS</i> 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 <i>CHS</i> induction in elicited soybean cells, suggesting that protein phosphorylation is involved in induction of the <i>CHS</i> signal pathway. Phosphorylation assays indicated that SBZ1 is phosphorylated <i>in vitro</i> in a soybean cell extract, and that this phosphorylation depends on Ca<sup>2+</sup>. Furthermore, recombinant soybean CDPK and the α subunit of CKII phosphorylate SBZ1 <i>in vitro</i>. 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.
- Plant biotechnology
Plant biotechnology 25(2), 131-140, 2008-03-01
Japanese Society for Plant Cell and Molecular Biology