The tobacco bZIP transcription factor BZI-1 binds to G-box elements in the promoters of phenylpropanoid pathway genes in vitro, but it is not involved in their regulation in vivo

Abstract

Screening of a tobacco (Nicotiana tabacum) cDNA library resulted in the isolation of a clone encoding the bZIP transcription factor BZI-1. With respect to amino acid sequence, conservation of protein domains, genomic exon-intron structure and expression pattern, BZI-1 is closely related to CPRF2, OHP1/2, BLZ1 and REB, a group of bZIP proteins which have been described in a number of dicot and monocot species. BZI-1 exhibits the characteristics of a transcription factor. It binds to G-box and C-box cis-elements in vitro, it is localised in the nucleus, and the N-terminal region of BZI-1 functions as an activation domain in both yeast and plant cells. Since BZI-1-related transcription factors have been isolated from dicots by in vitro binding to G-box elements in the chalcone synthase ( CHS) promoter, it has been suggested that phenylpropanoid pathway genes, such as CHS and PAL (phenylalanine ammonia-lyase), are targets of these proteins in vivo. However, after infection with Pseudomonas syringae or Tobacco Mosaic Virus, no changes in pathogen-induced PAL expression were observed in transgenic plants expressing increased levels of BZI-1 or a dominant negative form of the protein, BZI-1-DeltaN. In contrast to the tissue-specific expression of CHS and PAL, BZI-1 was found to be ubiquitously expressed in tobacco plants. Furthermore, no changes in the tissue-specific expression of PAL or CHS were observed in plants that were transgenic for BZI-1-DeltaN. Expression of a VP16-BZI-1 fusion protein would be expected to result in constitutive activation of the BZI-1 target genes. However, tetracycline-dependent expression of a VP16-BZI-1 protein in tobacco plants did not result in activation of CHS or PAL. On the basis of these data, we conclude that the phenylpropanoid pathway genes analysed are not targets of BZI-1 in vivo. Thus, the pattern of in vitro DNA binding of transcription factors need not always reflect their in vivo function.

TheArabidopsisGRAS Protein SCL14 Interacts with Class II TGA Transcription Factors and Is Essential for the Activation of Stress-Inducible Promoters

“…RNA gel blots were prepared and hybridized as described by Heinekamp et al (2002). Probes were amplified from either cDNA or plasmid templates using appropriate primers for SCL14/At1g07530, GUS, PR-1/At2g14610, and GST6/At2g47730 (see Supplemental Table 4 online).…”

Identification and Regulation of TPS04/GES, anArabidopsisGeranyllinalool Synthase Catalyzing the First Step in the Formation of the Insect-Induced Volatile C16-Homoterpene TMTT

“…Total RNA was extracted using the Trizol method (Invitrogen) and analyzed by RNA gel blot analysis as described (Heinekamp et al, 2002). An 846-bp GES-specific probe was amplified by PCR using the primer combination P12 and P13 (see Supplemental Table 3 online for primer sequences).…”

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

“…Parsley CPRF2, maize OHP1/2, rice REB, barley BLZ, and BZI-1 form a small group of transcription factors that are functionally homologous (Heinekamp et al 2002). SBZ1 contains some features that are highly conserved in these transcription factors ( Figure 1A), including the amino acid sequence, domain structures (D1-D4), DNAbinding domains (basic domain), leucine zipper domains, and N-terminal proline-rich putative activation domains, suggesting that SBZ1 belongs to this group.…”

“…D3 is adjacent to the bZIP region, and D4, which comprises the CDPK substrate motif (L-X-R-X-X-S/T-V-X-X-L), is located near the Cterminus. SBZ1 also contains a proline-rich region, predicted to be a transactivation domain, near the Nterminus (Heinekamp et al 2002). Several putative CKII phosphorylation sites (S-X-X-D/E) are present, with one located in D2, and the basic domain is also conserved among this group of transcription factors.…”

“…At first, G/HBF-1 was described to be isolated from soybean (Dröge-Laser et al 1997), however it was revised that the isolated cDNA clone was originated from tobacco, and was found not to be full-length. Then the full-length cDNA for a tobacco bZIP protein was isolated and deginated BZI-1 (Heinekamp et al 2002). BZI-1 is closely related to common plant regulatory factor 2 (CPRF2) from parsley.…”