Arabidopsis bZIP Protein HY5 Directly Interacts with Light-Responsive Promoters in Mediating Light Control of Gene Expression

Abstract

The Arabidopsis HY5 gene has been defined genetically as a positive regulator of photomorphogenesis and recently has been shown to encode a basic leucine zipper type of transcription factor. Here, we report that HY5 is constitutively nuclear localized and is involved in light regulation of transcriptional activity of the promoters containing the G-box, a well-characterized light-responsive element (LRE). In vitro DNA binding studies suggested that HY5 can bind specifically to the G-box DNA sequences but not to any of the other LREs present in the light-responsive promoters examined. High-irradiance light activation of two synthetic promoters containing either the consensus G-box alone or the G-box combined with the GATA motif (another LRE) and the native Arabidopsis ribulose bisphosphate carboxylase small subunit gene RBCS-1A promoter, which has an essential copy of the G-box, was significantly compromised in the hy5 mutant. The hy5 mutation's effect on the high-irradiance light activation of gene expression was observed in both photosynthetic and nonphotosynthetic tissues. Furthermore, the characteristic phytochrome-mediated red light- and far-red light-reversible low-fluence induction of the G-box-containing promoters was diminished specifically in hy5 plants. These results suggest that HY5 may interact directly with the G-box in the promoters of light-inducible genes to mediate light-controlled transcriptional activity.

A Clock- and Light-Regulated Gene That Links the Circadian Oscillator to LHCB Gene Expression

“…These results show that the expression of the ZGT gene is light inducible and further suggest that the regulation of its photoresponsiveness occurs at least partially via changes in transcriptional rates. These results are consistent with the hypothesis that the G/E box in the ZGT promoter is recognized by light-regulated transcription factors such as PIF3 (Martínez-García et al, 2000) and HY5 (Chattopadhyay et al, 1998).…”

“…Phytochrome B binds reversibly to G-box-bound PIF3 upon light-triggered conversion of phytochrome B to its biologically active conformer. A similar story has been reported for the bZIP protein factor, HY5 (Chattopadhyay et al, 1998). The presence in the ZGT promoter of this core G-box element for light signaling is consistent with a role in the light regulation of ZGT by PIF3 and/or HY5.…”

“…Between positions Ϫ 147 and Ϫ 142 of the ZGT 5 Ј flanking region, we found a palindromic hexanucleotide DNA sequence, CACGTG, that is one version of the light-regulated motif known as a G-box core (Chattopadhyay et al, 1998;Martínez-García et al, 2000). Within the 680-bp 5 Ј flanking region of the Arabidopsis p ZGT gene, we also found four putative G-box motifs located at Ϫ 84 to Ϫ 79, Ϫ 263 to Ϫ 258, Ϫ 334 to Ϫ 321, and Ϫ 675 to Ϫ 670 relative to the first codon (numbered as ϩ 1) of its putative translational start site.…”

ABA receptor PYL9 promotes drought resistance and leaf senescence

“…In this study, we evaluated the drought resistance of 14 transgenic Arabidopsis-overexpressing PYLs driven by the constitutive 35S cauliflower mosaic virus (CaMV) promoter, the stress-inducible RD29A promoter, the guard cell-specific GC1 and ROP11 promoters (20,21), and the green tissue-specific ribulose bisphosphate carboxylase small subunit (RBCS) RBCS-1A promoter (22). We found that, relative to the WT and all other combinations, pRD29A::PYL9 transgenic Arabidopsis plants had both greater drought resistance and accelerated drought-or ABA-induced leaf senescence.…”

Light Regulation of Nitrate uptake, Assimilation and Metabolism

“…The HY5 locus encodes a bZIP transcription factor known to be important for deetiolation and expression of several genes related to photosynthesis. In Arabidopsis the HY5 protein binds to Light Responsive Elements (LRE) in promoters, for instance a Gbox (Chattopadhyay et al 1998). HY5 degradation is stimulated by another protein, COP1.…”