Abstract
The etiolation process, which occurs after germination, is terminated once light is perceived and then de-etiolation commences. During the de-etiolation period, monochromatic lights (blue, red and far-red) induce differences in gene expression profiles and plant behavior through their respective photoreceptors. ELONGATED HYPOCOTYL 5 (HY5), a bZIP-type transcription factor (TF), regulates gene expression in the de-etiolation process, and other bZIP TFs are also involved in this regulation. However, transcriptomic changes that occur in etiolated seedlings upon monochromatic light irradiation and the relationship with the bZIP TFs still remain to be elucidated. Here, we track changes in the transcriptome after exposure to white, blue, red and far-red light following darkness and reveal both shared and non-shared trends of transcriptomic change between the four kinds of light. Interestingly, after exposure to light, HY5 expression synchronized with those of the related bZIP TF genes, GBF2 and GBF3, rather than HY5 HOMOLOG (HYH). To speculate on the redundancy of target genes between the bZIP TFs, we inspected the genome-wide physical binding sites of homodimers of seven bZIP TFs, HY5, HYH, GBF1, GBF2, GBF3, GBF4 and EEL, using an in vitro binding assay. The results reveal large overlaps of target gene candidates, indicating a complicated regulatory literature among TFs. This work provides novel insight into understanding the regulation of gene expression of the plant response to monochromatic light irradiation.
Highlights
Light is an essential source of energy production in plants but is a key signal for the beginning of proper morphogenesis
Downstream signaling pathways after light perception are thought to be different between photoreceptors, but the signaling cascades from respective photoreceptors converge on a basic/leucine zipper-type transcription factor, ELONGATED HYPOCOTYL 5 (HY5) [3]
Clustering analysis using whole gene expression profiles showed an apparent time-dependent similarity in the profiles of the four kinds of light (Figure 1C). This analysis indicated that red and far-red light, rather than blue light, were relatively closely clustered. This result is consistent with the fact that both red and far-red light pass through the same photoreceptors and blue light is perceived through different ones [2]
Summary
Light is an essential source of energy production in plants but is a key signal for the beginning of proper morphogenesis. Perception of light after germination is the first turning point for plants, because it triggers morphogenesis, including inhibition of hypocotyl elongation and expansion of cotyledons. This step is called photomorphogenesis [1]. It has been reported that GBF2 localizes in the cytoplasm in the dark but moves into the nucleus in response to blue light, indicating its involvement in light signaling [17]. It is unknown whether GBF3 acts in the light response, it is known to enhance ABA insensitivity and drought tolerance [18,19]. We believe that our results will help to expand the knowledge of the monochromatic light response
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