Project description:The transcription factor HY5 acts downstream of multiple families of the photoreceptors and promotes photomorphogenesis. Although it is well accepted that HY5 acts to regulate target gene expression, in vivo binding of HY5 to any of its target gene promoters has yet to be demonstrated. Here we used a chromatin immunoprecipitation procedure to verify suspected in vivo HY5 binding sites. We demonstrated that in vivo association of HY5 with promoter targets is not altered under distinct light qualities or during light-to-dark transition. Coupled with DNA chip hybridization using high density 60-nucleotide oligomer microarray that contains one probe for every 500 nucleotides over the entire Arabidopsis genome, we mapped genome wide in vivo HY5 binding sites. This analysis showed that HY5 binds preferentially to promoter regions in vivo and revealed over 3 thousand chromosomal sites as putative HY5 binding targets. HY5 binding targets tend to be enriched in the early light responsive genes and transcription factor genes. Our data thus supports a model in which HY5 is a high hierarchical regulator of the transcriptional cascades for photomorphogenesis. Keywords: ChIP-chip
Project description:Cryptochromes (CRYs) is known as the key blue light receptors that promote photomorphogenesis in Arabidopsis, but to date, the underlying mechanisms are still not fully understood. Through interrogating the CRY2 interactome, we identified MOS4-ASSOCIATED COMPLEX subunits 3A and 3B (MAC3A and MAC3B) as blue light-independent CRY2 interacting partners. MAC3A/B proteins could be assembled into liquid nuclear condensates of CRYs in a blue light-dependent manner. Hypocotyl elongation is markedly repressed in mac3ab double knock-out mutants under various light conditions, which uncovers a previously unknown role of MAC3A/B as negative regulators in plant photomorphogenesis. Our results also uncover the noncanonical activities of MAC3A as the DNA-binding proteins that regulate transcription. Genome-wide mapping of MAC3A-binding sites reveals that blue light facilitates the binding of MAC3A to its targets, which is weakened in cry1cry2 mutants, suggesting that CRYs may enhance MAC3A activities in blue light to negatively influence photomorphogenesis. Interestingly, we observe that the genomic binding sites of MAC3A and HY5 are largely overlapped, and physical interactions between MAC3A and HY5 are detected as well. In addition, the in vitro DNA-binding assay shows that both proteins compete for the same DNA probe. These results indicate that MAC3A may antagonize the function of HY5 by competing for the common binding sites across the genome. Taken together, we propose that cryptochromes may fine-tune Arabidopsis photomorphogenesis by balancing the positive and negative effects on HY5 activities.
Project description:LONG HYPOCOTYL 5 (HY5) is a basic leucine zipper transcription factor (TF) that functions downstream of multiple families of photoreceptors. Mutations in the HY5 gene cause a myriad of aberrant phenotypes in Arabidopsis, including elongated hypocotyl, reduced accumulation of pigments, halted chloroplast development in greening hypocotyls, altered root morphology and defective hormonal and stimulus responses. HY5 thus acts as an integrater that links various gene networks to coordinate plant development. Here we report an effort to experimentally map the HY5-mediated gene networks in Arabidopsis by integrating genomic loci occupied by HY5 and HY5-dependent gene expression profiles. Our results indicate HY5 binds to over 9,000 genes, which detectably impact the expression of over 1,100 genes, either positively or negatively. Further, HY5 indirectly regulates many other genes through sub-networks mediated by other regulators. In particular, we show that HY5 regulates eight microRNA (miRNA) genes, which in turn control transcript abundance of specific target genes. Over-expressing the HY5-targeted miR408 resulted in phenotypes that are opposite to hy5 mutants. Together our results revealed both the transcriptional and post-transcriptional components of the HY5-mediated gene networks responsible for the phenotypic complexity in plants. Chromatin isolation was performed with 4-day-old whole seedlings grown under wild type light (WL) or 8hr darkness treatment according to Bowler et al. (2004). The resuspended chromatin pellet was sonicated at 4M-BM-0C with a Diagenode Bioruptor set at high intensity for 10 min (30 s on, 30 s off intervals). The DNA was sheared to an average size of approximately 500 bp. Chromatin was immunoprecipitated, washed, reverse cross-linked, amplified, and hybridized according to the Affymetrix Chromatin Immunoprecipitation Assay Protocol Rev.3. A polyclonal HY5 antibody purified from anti-HY5 rabbit IgG using Sepharose 4B beads coupled with purified recombinant HY5 protein was used. M-bM-^@M-^XFlow-throughM-bM-^@M-^Y IgG devoid of the HY5 antibody was used as a negative control. An aliquot of untreated sonicated chromatin was reverse cross-linked and used as a total input DNA control for ChIP-PCR experiments. Four biological replicates for each experimental condition and two biological replicates for each control condition were hybridized to tiling arrays, resulting in a total of 12 chips.
Project description:To determine the functional relevance of the HY5 binding sites to the transcriptional regulation, we performed genome wide expression analysis using WT and hy5 grown in continuous white light for 4 days. Keywords: mutant/widetype comparative
Project description:Injured plant somatic tissues regenerate themselves by establishing the shoot or root meristems. In Arabidopsis (Arabidopsis thaliana) a two-step culture system ensures regeneration by first promoting the acquisition of pluripotency and subsequently specifying the fate of new meristems. Although previous studies have reported the importance of phytohormones auxin and cytokinin in determining the fate of new meristems, it remains elusive whether and how the environmental factors influence this process. In this study, we investigated the impact of light signals on shoot regeneration using Arabidopsis hypocotyl as explants. We found that light signals promote shoot regeneration while inhibiting root formation. ELONGATED HYPOCOTYL 5 (HY5), the pivotal transcriptional factor in light signaling, plays a central role in this process by mediating the expression of key genes controlling the fate of new meristems. Specifically, HY5 directly represses root development genes and activates shoot meristem genes, leading to the establishment of shoot progenitor from pluripotent callus. We further demonstrated that the early activation of photosynthesis is critical for shoot initiation, and this is transcriptionally regulated downstream of the HY5-dependent pathways. In conclusion, we uncovered the intricate molecular mechanisms by which light signals control the establishment of new meristem through the regulatory network governed by HY5, thus, highlighting the influence of light signals on plant developmental plasticity.