Genome-wide analysis of gene expression reveals function of the bZIP transcription factor HY5 in the UV-B response of Arabidopsis

Abstract

The light environment is a key factor that governs a multitude of developmental processes during the entire life cycle of plants. An important and increasing part of the incident sunlight encompasses a segment of the UV-B region (280 -320 nm) that is not entirely absorbed by the ozone layer in the stratosphere of the earth. This portion of the solar radiation, which inevitably reaches the sessile plants, can act both as an environmental stress factor and an informational signal. To identify Arabidopsis genes involved in the UV response, we monitored the gene expression profile of UV-B-irradiated seedlings by using high-density oligonucleotide microarrays comprising almost the full Arabidopsis genome (>24,000 genes). A robust set of early low-level UV-Bresponsive genes, 100 activated and 7 repressed, was identified. In all cases analyzed, UV-B induction was found to be independent of known photoreceptors. This group of genes is suggested to represent the molecular readout of the signaling cascade triggered by the elusive UV-B photoreceptor(s). Moreover, our analysis identified interactions between cellular responses to different UV-B ranges that led us to postulate the presence of partially distinct but interacting UV-B perception and signaling mechanisms. Finally, we demonstrate that the bZIP transcription factor HY5 is required for UV-B-mediated regulation of a subset of genes.

Arabidopsis STO/BBX24 negatively regulates UV-B signaling by interacting with COP1 and repressing HY5 transcriptional activity

“…Recently, significant progress has been made in our understanding of the UV-B response pathway in Arabidopsis, which involves the UV-B photoreceptor UVR8 [9], two positive regulators COP1 [12] and HY5 [23], and two WD40-repeat-containing proteins, RUP1 and RUP2 that negatively regulate the pathway [24]. In this study, we identified BBX24 as a new negative regulator of UV-B responses in Arabidopsis.…”

“…The essential role of HY5 in UV-B signaling [23] encouraged us to examine whether BBX24 physically interacts with HY5. Full-length HY5 fused with the GAL4-DNA-binding domain interacted strongly with the BBX24 fused with the GAL4-activation domain in the yeast two-hybrid system ( Figure 3A).…”

“…Because HY5 is an essential transcription factor in UV-B responses [23], we then analyzed whether BBX24 can affect HY5's transcriptional activity in a transient assay under UV-B. For this purpose, HY5 was expressed as a fusion protein with the GAL4-DNA-binding domain under the control of a 35S promoter ( Figure 4B).…”

Genome-Wide Gene Expression Analysis Reveals a Critical Role for CRYPTOCHROME1 in the Response of Arabidopsis to High Irradiance

“…Expression analysis of the cry1 and hy5 mutants during early light development or following a shift from darkness to light has been performed previously (Ma et al, 2001;Holm et al, 2002;Folta et al, 2003;Jiao et al, 2003;Ohgishi et al, 2004;Ulm et al, 2004). However, a direct comparison between our experiment and published results is difficult due to the usage of very different plant material.…”

Grapevine Biotechnology: Molecular Approaches Underlying Abiotic and Biotic Stress Responses

“…Following monomerization, UVR8 accumulates in the nucleus and interacts with the positive regulator Constitutively Photomorphogenic 1 (COP1) [139][140][141][142], a WD40/RING-E3 ubiquitin ligase that in non-inductive conditions targets HY5 (Elongated Hypocotyl 5) for proteosome-dependent degradation [143]. HY5 is a key effector of UV-B protection and light photomorphogenic responses [144,145], and it is transcriptionally activated by UV-B in a UVR8-and COP1-dependent manner [146][147][148]. Other components of the UVR8 signalling pathway are repressor of UV-B photomorphogenesis 1 (RUP1) and RUP2.…”