Researchers from the Instituto de Tecnologia Qu?­mica e Biol??gica Ant??nio
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 riceflowering 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.

A new light in rice flowering â?? ITQB (unl.pt)
[www.itqb.unl.pt]