Photomorphogenesis is critical for seedling development. Buried seed germinates and develop into etiolated seedling with long hypocotyl, closed cotyledons and curved apical hook. Once seedling reaches soil surface, the elongation of hypocotyl is quickly inhibited, and cotyledons are open and expand in response to light. Plants have evolved sensitive signal transduction systems to fine-tune photomorphogenesis in response to the changes of light environments. Among them, the COP1–HY5 module is the central hub for integrating diverse light signals.
A group led by Dr. Hongtao Liu from CAS Center for Excellence in Molecular Plant Sciences now identify two new proteins, named COR27 and COR28, act as key regulators in the COP1–HY5 regulatory hub by ensuring proper skotomorphogenic growth in the dark and photomorphogenic development in the light.
COLD REGULATED (COR) genes, COR27 and COR28, are involved in the diverse biological processes such as circadian clock, freezing tolerance, and flowering time. It has been shown that light and temperature coordinately regulate their expression. Interestingly, blue light has been also found to stabilize the COR27 and COR28 at protein level. However, its underlying mechanism is unknown. Liu and her colleagues show that COR27 and COR28 physically interact with COP1 and this interaction is responsible for their degradation in the dark. Functional analysis indicates that COR27 and COR28 promote hypocotyl elongation and act as negative regulators of photomorphogenesis. COR27 interacts with HY5, and directly associates with the promoters of the HY5 target genes. Consistently, genome-wide gene expression analysis shows that HY5, COR27, and COR28 co-regulate many common genes. Their results collectively demonstrate that light promotes the accumulation of HY5 and COR27, while COR27 physically interacts with HY5 to inhibit its transcriptional activity and fine-tune skotomorphogenesis development in the dark and photomorphogenic development in the light.
This work entitled “COR27 and COR28 are Novel Regulators of the COP1–HY5 Regulatory Hub and Photomorphogenesis in Arabidopsis” has been published online in The Plant Cell on August 7^th, 2020. The research was funded by NSFC, MOST and CAS.

A hypothetical model depicting COP1 regulates COR27, COR28 degradation and COR27, COR28 interact with HY5 to regulate gene expression and photomorphogenesis in Arabidopsis.

COR27 and COR28 are negative regulators of photomorphogenesis. COR27 and COR28 undergo COP1-mediated degradation in darkness. COR27 inhibits the transcriptional activity of HY5 even in darkness to promote skotomorphogenic growth. Light promotes the accumulation of HY5 and COR27, while COR27 physically interacts with HY5 to inhibit its transcriptional activity and fine-tune photomorphogenic development in the light.

Link: https://doi.org/10.1105/tpc.20.00195
Contact:
Dr. Hongtao Liu, Professor
National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences/Shanghai Institute of Plant Physiology and Ecology (SIPPE), Chinese Academic of Sciences
Tel: 86-21-54924291
Email: htliu@cemps.ac.cn