Abstract
Abscisic acid (ABA) is recognized as the key hormonal regulator of plant stress physiology. This phytohormone is also involved in plant growth and development under normal conditions. Over the last 50 years the components of ABA machinery have been well characterized, from synthesis to molecular perception and signaling; knowledge about the fine regulation of these ABA machinery components is starting to increase. In this article, we review a particular regulation of the ABA machinery that comes from the plant circadian system and extends to multiple levels. The circadian clock is a self-sustained molecular oscillator that perceives external changes and prepares plants to respond to them in advance. The circadian system constitutes the most important predictive homeostasis mechanism in living beings. Moreover, the circadian clock has several output pathways that control molecular, cellular and physiological downstream processes, such as hormonal response and transcriptional activity. One of these outputs involves the ABA machinery. The circadian oscillator components regulate expression and post-translational modification of ABA machinery elements, from synthesis to perception and signaling response. The circadian clock establishes a gating in the ABA response during the day, which fine tunes stomatal closure and plant growth response.
Highlights
Regulation at Multiple Levels.Abscisic acid (ABA) is a phytohormone involved in the plant stress response as well as plant growth and development
We focus this review on the regulation of ABA machinery by the plant circadian clock
These observations indicate a possible regulation of ABA synthesis by the circadian clock
Summary
The circadian clock is a self-sustained molecular oscillator present in each plant cell [9,10,11,12], hierarchical in nature at tissue level [13]. Circadian oscillations are efficiently entrained by daily light/dark changes. This environmental photic diurnal cycle acts as a ‘zeitgeber’, or time giver, and induces the clock’s diurnal synchrony to 24 h [14]. Output pathways control molecular, cellular and physiological downstream processes, such as hormonal responses, transcriptional activity, the cell cycle and growth, among others [14,15,16,17].
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