ABA Signaling and Circadian Clock - Abscisic Acid: Metabolism, Transport and Signaling - page 374

Chapter 19
ABA Signaling and Circadian Clock

Sergi Portolés and Da-Peng Zhang

Abstract The circadian clock is an endogenous timing mechanism that controls a
variety of physiological, metabolic, and developmental process. It serves as a time-
keeper allowing the organisms to predict recurrent environmental variations, ensur-
ing that the onset of key processes coincides with appropriate conditions. In plants,
the use of genome-wide approaches revealed that clock-regulated genes are overrep-
resented in several plant hormones and stress-responsive pathways, especially those
related with abscisic acid (ABA). Concretely, the circadian clock controls the daily
fluctuations in ABA concentration and modulates plant sensitivity to this hormone
in a process called gating. In turn, changes in ABA levels due to stressful condi-
tions feed back the clock by modifying its pace. Emerging findings have proven that
ABA and circadian clock reciprocal regulation is essential to integrate internal and
external cues to properly adjust key physiology and development processes such as
flowering transition, seed dormancy and germination, and abiotic and biotic stress
responses. This mutual regulation is crucial for plant fitness and survival as allows to
anticipate and precisely respond to predictable stressful conditions.

Keywords ABA signaling · Circadian clock · Cross talk

19.1 Circadian Clock

Day and night cycles, as a result of the Earth's rotation over its axis, lead to drastic
changes in the environmental conditions, challenging the life since the beginning of
the evolution. For this reason, the living organisms have adapted their physiological,