ABA and the Floral Transition - Abscisic Acid: Metabolism, Transport and Signaling - page 354

Chapter 18
ABA and the Floral Transition

Lucio Conti, Massimo Galbiati and Chiara Tonelli

Abstract Plants use endogenous and environmental cues to trigger flowering.
While variations in day length and temperature play a major role in controlling
the transition to flowering, little is known about water stress-derived signals.
Drought conditions cause early flowering in various plant species. Since it is well
recognized that drought conditions also stimulate abscisic acid (ABA) accumu-
lation, ABA signalling might underpin the observed early flowering response.
Experiments have shown that exogenous applications of ABA cause flowering
time alterations, suggesting that ABA might be an endogenous component affect-
ing the floral transition. Confirming a role for endogenous ABA in flowering,
mutants impaired in ABA production display flowering alterations, although a
consensus as to the precise mode of action of ABA in plants is lacking. ABA acti-
vates flowering in several plant species and in Arabidopsis it promotes activation
of the key floral gene FLOWERING LOCUS T . However, how ABA signalling is
integrated in the floral network remains poorly understood. The evidence reviewed
here suggests that ABA activates a complex network of signalling components
including transcription factors with contrasting effects in flowering. Lesions in
these ABA-Photoperiod interaction signalling genes produce alterations in flower-
ing but their regulation and site of action have been so far elusive. ABA is mainly
known as a stress hormone and its role in flowering is only beginning to emerge.
In this chapter we will review the evidence for and against ABA controlling the
floral transition.

Keywords ABA · Floral transition · ABA-Photoperiod interaction