Abstract
Cryptochromes are blue light photoreceptors involved in development and circadian clock regulation. They are found in both eukaryotes and prokaryotes as light sensors. Long Hypocotyl in Far-Red 1 (HFR1) has been identified as a positive regulator and a possible transcription factor in both blue and far-red light signaling in plants. However, the gene targets that are regulated by HFR1 in cryptochrome 1 (cry1)-mediated blue light signaling have not been globally addressed. We examined the transcriptome profiles in a cry1- and HFR1-dependent manner in response to 1 hour of blue light. Strikingly, more than 70% of the genes induced by blue light in an HFR1-dependent manner were dependent on cry1, and vice versa. High overrepresentation of W-boxes and OCS elements were found in these genes, indicating that this strong cry1 and HFR1 co-regulation on gene expression is possibly through these two cis-elements. We also found that cry1 was required for maintaining the HFR1 protein level in blue light, and that the HFR1 protein level is strongly correlated with the global gene expression pattern. In summary, HFR1, which is fine-tuned by cry1, is crucial for regulating global gene expression in cry1-mediated early blue light signaling, especially for the function of genes containing W-boxes and OCS elements.
Highlights
Light is an energy source for photosynthesis, it is an important signal for plant development
We propose that Hypocotyl in Far-Red 1 (HFR1) may elevate downstream gene expression through Wboxes and OCS elements, indicating that a subset of genes, having either of these cis-elements, may be responsive to cry1-mediated early blue light signaling
It has been shown that the expression profiles under different light qualities are similar to each other [21]; indicating that photomorphogenesis, mediated by the Figure 5. cry1 influences HFR1 on both RNA and protein level. (A) RT-PCR showing the relative expression level of HFR1 normalized to GAPDH
Summary
Light is an energy source for photosynthesis, it is an important signal for plant development. HFR1 was originally identified based on its role in inhibition of hypocotyl elongation, cotyledon expansion, modulation of gravitropic growth, and induction of certain light-regulated gene expression in phyA signaling [13,14,15]. De-etiolation in hfr mutants is significant under high fluence rates It is still unknown how HFR1 identifies its downstream targets and what they are. HFR1’s function in anthocyanin accumulation is most likely to be affected by a complex combination of cry, cry and phyA [6] It is still a puzzle how HFR1 integrates different light signals and distinguishes them from each other. We propose that HFR1 may elevate downstream gene expression through Wboxes and OCS elements, indicating that a subset of genes, having either of these cis-elements, may be responsive to cry1-mediated early blue light signaling
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