Research Reveals the Light Mechanism that Regulates Rice Flowering Time

Researchers from the Instituto de Tecnologia Química e Biológica António Xavier da Universidade NOVA de Lisboa (ITQB NOVA), Leibniz Institute of Vegetable and Ornamental Crops (IGZ) and the Institute of Biochemistry and Biology and Potsdam University have clarified the role of the photoperiod and circadian clock components in regulating rice flowering time.

The circadian clock is present in most living beings. In plants, the circadian clock and light signals result in photoperiodism, the physiological response to light periods that influence flowering time. Photoperiodism varies between species so Arabidopsis thaliana needs short nights to flower, while rice requires long nights. This study revealed that, in rice, it is the light receptor phytochrome B that makes the connection between light and the Evening Complex, thus regulating the flowering time. The Evening Complex is a component of the circadian clock and consists of a group of proteins that are active during the night and that regulate proteins linked to flowering.

The research team found that when activated by light, phytochrome B inactivates EARLY FLOWERING 3-1 (ELF3-1), one of the Evening Complex proteins. This leads to repression of flowering, and later to late flowering. The researchers also showed that in phytochrome B mutants, the ELF3-1 protein is always active during day and night, and these plants flowered much earlier. The study also clarifies the crucial role that the Evening Complex plays in flowering.

Through the CRISPR-Cas9 technique, the researchers studied rice variants with inactive Evening Complex proteins, including ELF3-1, ELF3-2, and LUX ARRHYTHMO (LUX). They found that plants without the Evening Complex components never flowered, regardless of the duration of light periods, leading the research team to conclude that the activity of this complex is essential to induce flowering in rice.

For more details, read the news article on the ITQB NOVA website.