GI is a repressor of ABA transcriptional responses and sensitivity in Arabidopsis

Transcriptional reprogramming plays a key role in drought stress responses, preceding the onset of morphological and physiological adaptations. The best characterised signal regulating gene expression in response to drought is the phytohormone abscisic acid (ABA). ABA-regulated gene expression, biosynthesis and signalling are highly organised in a diurnal cycle, so that ABA-regulated physiological traits occur at the appropriate time of the day. The mechanisms that underpin such diel oscillations in ABA signals are poorly characterised. Here we uncover GIGANTEA (GI) as a key gate keeper of ABA-regulated transcriptional and physiological responses. Time-resolved RNAseq under different irrigation scenarios indicate that gi mutants produce an exaggerated ABA response at midday, despite accumulating wild-type levels ABA. The direct comparison with ABA-deficient mutants confirms the role of GI in controlling ABA-regulated genes and enabled us to distinguish a phase of high ABA sensitivity at dawn, characterized by low GI accumulation. Overall design: Analysis of RNAsequencing data in different irrigation conditions and genetic backgrounds