GIGANTEA Enables Drought Escape Response via Abscisic Acid-Dependent Activation of the Florigens and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1

Abstract

Modulation of the transition to flowering plays an important role in the adaptation to drought. The drought-escape (DE) response allows plants to adaptively shorten their life cycle to make seeds before severe stress leads to death. However, the molecular basis of the DE response is unknown. A screen of different Arabidopsis (Arabidopsis thaliana) flowering time mutants under DE-triggering conditions revealed the central role of the flower-promoting gene GIGANTEA (GI) and the florigen genes FLOWERING LOCUS T (FT) and TWIN SISTER OF FT (TSF) in the DE response. Further screens showed that the phytohormone abscisic acid is required for the DE response, positively regulating flowering under long-day conditions. Drought stress promotes the transcriptional upregulation of the florigens in an abscisic acid-and photoperiod-dependent manner, so that early flowering only occurs under long days. Along with the florigens, the floral integrator SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 is also up-regulated in a similar fashion and contributes to the activation of TSF. The DE response was recovered under short days in the absence of the floral repressor SHORT VEGETATIVE PHASE or in GI-overexpressing plants. Our data reveal a key role for GI in connecting photoperiodic cues and environmental stress independently from the central FT/TSF activator CONSTANS. This mechanism explains how environmental cues may act upon the florigen genes in a photoperiodically controlled manner, thus enabling plastic flowering responses.

A Drought-Inducible Transcription Factor Delays Reproductive Timing in Rice

“…Moreover, other environmental cues also differentially affect their flowering behavior upon water scarcity. The study of Arabidopsis showed that drought-induced acceleration of flowering is dependent on LD condition (Han et al, 2013;Riboni et al, 2013). Our study in rice showed that drought delayed flowering is photoperiod independent, while other factors such as light intensity or temperature may affect the severity of drought-delayed flowering time mediated by OsABF1 (Fig.…”

“…Because drought triggers phytohormone abscisic acid (ABA) biosynthesis and signal transduction, it has been proposed that ABA mediates DE response. Consistent with this hypothesis, an ABA biosynthesis knockout mutant, aba1-6, was shown to flower later under LDs (Riboni et al, 2013). External application of ABA also delays flowering (Cheng et al, 2002;Achard et al, 2006;Domagalska et al, 2010;Wang et al, 2013), suggesting a dual effect of ABA on floral transition.…”

“…For example, Arabidopsis has a short life cycle and naturally grows in xeric environments, so it relies on DE response when encountering drought stress (Supplemental Fig. S9) (Riboni et al, 2013). In contrast, lowland rice is historically grown in mesic conditions and tends to delay flowering in response to temporary drought stress (Wopereis et al, 1996;Ndjiondjop et al, 2010).…”

“…Interestingly, drought accelerates flowering of Arabidopsis only under LDs but not SDs. Genetic studies have revealed that GIGANTEA (GI) knockout abolishes the drought-induced early flowering behavior of Arabidopsis under LDs (Han et al, 2013;Riboni et al, 2013), but the mechanism of GI-mediated photoperiod-dependent DE response has not been elucidated. The biological networks connecting drought perception, ABA signaling, and flowering gene regulation also remain unclear.…”

Allelic polymorphism of GIGANTEA is responsible for naturally occurring variation in circadian period in Brassica rapa

“…Recently, GI has been implicated in cold (25), oxidative (26), drought (27), and salt (28) stress tolerance. Accordingly, we tested our panel of Arabidopsis gi-201 mutants carrying the B. rapa GI alleles for freezing tolerance, as measured by electrolyte leakage after exposure to freezing temperatures.…”