Abstract
Drought is one of the most critical environmental stresses limiting plant growth and crop productivity. The synthesis and signaling of abscisic acid (ABA), a key phytohormone in the drought stress response, is under photoperiodic control. GIGANTEA (GI), a key regulator of photoperiod-dependent flowering and the circadian rhythm, is also involved in the signaling pathways for various abiotic stresses. In this study, we isolated ENHANCED EM LEVEL (EEL)/basic Leu zipper 12, a transcription factor involved in ABA signal responses, as a GI interactor in Arabidopsis (Arabidopsis thaliana). The diurnal expression of 9-CIS-EPOXYCAROTENOID DIOXYGENASE 3 (NCED3), a rate-limiting ABA biosynthetic enzyme, was reduced in the eel, gi-1, and eel gi-1 mutants under normal growth conditions. Chromatin immunoprecipitation and electrophoretic mobility shift assays revealed that EEL and GI bind directly to the ABA-responsive element motif in the NCED3 promoter. Furthermore, the eel, gi-1, and eel gi-1 mutants were hypersensitive to drought stress due to uncontrolled water loss. The transcript of NCED3, endogenous ABA levels, and stomatal closure were all reduced in the eel, gi-1, and eel gi-1 mutants under drought stress. Our results suggest that the EEL-GI complex positively regulates diurnal ABA synthesis by affecting the expression of NCED3, and contributes to the drought tolerance of Arabidopsis.
Highlights
The productivity and distribution of plants are adversely influenced by a variety of abiotic stresses, including drought, high salinity, and extreme temperatures (Zhu, 2016)
Genes did not differ in any of the genotypes tested (Supplementary Figure S3). These results suggest that EM LEVEL (EEL) and GI positively co-regulate the diurnal expression of NCED3 and NCED5, the later gene was observed only in the eel gi-1 double mutant
When leaves were exposed to dehydrating conditions, the stomata of the eel, gi-1, and eel gi-1 mutants closed much less than those of the WT (Figure 8C and 8D). These results indicated that the impaired stomatal closure of the eel, gi-1, and eel gi-1 mutants was mainly caused by their low levels of stressinduced abscisic acid (ABA)
Summary
The productivity and distribution of plants are adversely influenced by a variety of abiotic stresses, including drought, high salinity, and extreme temperatures (Zhu, 2016). Plants have evolved distinct morphological and physiological adaptations that reduce the adverse impact of water shortages (Basu et al, 2016; Gilbert and Medina, 2016; Zhu, 2016). These adaptations are predominantly mediated by endogenous plant hormones, abscisic acid (ABA) (Basu et al, 2016; Zhu, 2016). ABA is involved in the response to various environmental challenges, including salinity, freezing, water deficit, wounding, and pathogen attack, and plays a role in a wide range of developmental processes, such as seed germination, early seedling development, and reproduction (Finkelstein et al, 2002; Huang et al, 2008; Cutler et al., 2010; Cao et al, 2011; Hauser et al, 2011)
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