Blossoming early in a dry world: interaction of Abscisic-Acid and photoperiodic pathways in Arabidopsis thaliana

Drought caused the anticipation of flowering in the model plant Arabidopsis as well as in several crops, at the cost of productivity. The Abscisic Acid pathway, that responds to and relays drought stimuli, interacts genetically with the photoperiodic flowering one and in particular with its key component GIGANTEA (GI). Using BiFC and Co-IP we find that GI interacts physically with group A bZIP transcription factors – to different extend final effectors of the Abscisic Acid pathway – e.g. Abscisic Acid responsive elements-Binding Factors (ABFs). Using sequence and structural predictions we annotate GI and ABFs to explain their functions and interactions. On one hand, we hypothesize on how ABFs can act as activators under ABA signalling and on what could be the function of GI in this as it is found to be part of the ABA gene regulatory network. On the other hand, GI cold be annotated for the first time with an Armadillo domain and thus structural predictions of complexes between this domain and ABFs or ABFs in complex with their General Regulatory Factors partners are analysed in detail. The latter point is also explored with preliminary and ongoing interaction assays leveraging on mutated forms of bZIPs and with the Armadillo truncation of GI. We reconcile the resulting observations with unpublished data of our lab where GI affects the stability ABFs. Altogether we produce a working model to falsify the role of GI in ABFs transcriptional complexes. Further studies are needed to gain a detailed understanding of the complex systems under study at different levels. Still in-silico predictions together with literature data provide the basis for exciting and testable hypotheses, to unravel how drought signals are integrated into the photoperiodic flowering pathway and shed light on the key but long enigmatic GI.