Abstract
Plants undergo several important developmental transitions including flowering and senescence during their life cycle. Timing these transitions according to the environmental conditions increases plant fitness and productivity. The circadian clock senses various environmental cycles, including photoperiod, and synchronizes plant physiological processes to maximize plant fitness. Here, we propose that the cellular localization of GIGANTEA (GI), a key clock component, regulates leaf senescence and flowering in Arabidopsis thaliana. We show that GI, which connects the circadian clock with photoperiod-regulated flowering, induces leaf senescence depending on its subcellular localization. Overexpression of GI in the gi mutant rescued its delayed senescence phenotype but only when the GI protein was targeted to the nucleus, not when it was targeted to the cytosol. In the nucleus, EARLY FLOWERING 4 (ELF4) inhibited the binding of GI to ORESARA 1 (ORE1) promoter to regulate leaf senescence. GI also positively regulated the day-peak of ORE1 expression. These results indicate that like flowering, leaf senescence is also controlled by the location of GI in the cell. Taken together, our results suggest that ELF4 and GI act together to control flowering and senescence in Arabidopsis.
Highlights
Plants undergo important developmental events, such as flowering and senescence, during their life cycle (Huijser and Schmid, 2011)
EARLY FLOWERING 4 (ELF4) directly interacts with GI and inhibits its binding to the ORESARA 1 (ORE1) promoter. These results suggest that GI acts as a mediator to couple flowering with leaf senescence for enhancing plant fitness and productivity
We previously reported that ORE1 is under the control of the circadian clock, and the clock component, PRR9, binds to the ORE1 promoter to induce leaf senescence (Kim et al, 2018)
Summary
Plants undergo important developmental events, such as flowering and senescence, during their life cycle (Huijser and Schmid, 2011). One of the circadian clock components, GIGANTEA (GI), regulates photoperiod-dependent flowering in Arabidopsis thaliana. GI directly binds to the Nuclear-Localized GI Regulates Leaf Senescence promoter of CONSTANS (CO), a key flowering regulator, and activates CO expression. GI promotes CO expression, enabling it to reach peak expression levels, only under longday (LD) photoperiod, not under short-day (SD) photoperiod This coincidence between the environmental condition (LDs) and internal rhythm (circadian rhythm) promotes flowering in Arabidopsis, and is known as the external coincidence model (Sawa et al, 2008). GI must be transferred to the nucleus for activating CO expression (Kim et al, 2013a) In the nucleus, another clock component, EARLY FLOWERING 4 (ELF4), physically interacts with and sequesters the GI protein, which inhibits GI from binding to the CO promoter (Kim et al, 2013b). The subcellular localization of GI is important for regulating flowering time in Arabidopsis
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