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Crop Biotech Update

Biologists Identify Plant Clock Genes Regulating Circadian Rhythm

March 23, 2016

A team of biologists at Nagoya University's Institute of Transformative Bio-Molecules (ITbM) led by Narihito Nakamichi has uncovered that the clock genes produced by plants during the evening are regulated by clock proteins produced in the morning.

During the afternoon, plants ready themselves for the cold temperatures that follow sunset. In this manner, plants use their biological clock to respond beforehand to the changes in their surrounding environment that are caused by variation in time. "Since 2011, we have been trying to find the key factor that regulates the expression of the gene that is transcribed during the afternoon," says Nakamichi. The group used PSEUDO-RESPONSE REGULATOR 5 (PRR5), which is a clock gene of the model plant, Arabidopsis thaliana.

According to Nakamichi, they believed that CCA1, a clock protein generated during sunrise, binds to a specific DNA sequence involved in the expression of the target gene PRR5. They collected the CCA1 protein bound to DNA using Chromatin immunoprecipitation (ChIP), and analyzed the DNA sequence by rapid DNA sequencing. They were able to identify that the PRR5 gene appears in the regulatory region at a high frequency, and data suggested that the CCA1 protein directly acts towards the regulatory region of the PRR5 gene and has a major effect on it.

The research group also found the target DNA region of the CCA1 clock protein in the plant cell's chromosome. "We found many genes that are expressed in the evening nearby the DNA region that CCA1 binds to," explains Nakamichi. Some of these genes are responsible for the plant's responses to drought stress, transmission of the signals from the plant hormone, abscisic acid, regulation of the opening and closing of stomata, and production of wax. "The results of our studies suggest that the CCA1 protein induces these biological processes to occur at a specific time during the evening."

For more details, read the research highlights at the Nagoya University website.