Impact of the SnRK1 protein kinase on sucrose homeostasis and the transcriptome during the diel cycle

Sucrose Non-Fermenting1-Related Kinase1 (SnRK1) is an evolutionarily conserved protein kinase with key functions in energy management during stress responses in plants. To address a potential role of SnRK1 under non-stress conditions, we performed a metabolomic and transcriptomic characterization of 20 d-old rosettes of Arabidopsis SnRK1 gain- and loss-of-function mutants during the diurnal cycle. SnRK1 manipulation altered the slope of the correlation between sucrose and trehalose 6-phosphate (Tre6P). It also modulated the flux of carbon to the tricarboxylic acid cycle downstream of Tre6P-signalling. SnRK1 depletion modified expression of SnRK1-induced genes least at the end of the day (when Tre6P levels peak) and most at the end of the night (when Tre6P levels are lowest). Expression of a subset of these genes was attenuated by inducible Tre6P accumulation in a time-of-day dependent manner. Finally, transcriptional profiling uncovered a wide impact of SnRK1 on gene expression in non-stress conditions, establishing a clear connection with iron and sulfur metabolism. In conclusion, SnRK1 plays central functions in metabolic and transcriptional regulation in the absence of stress. SnRK1 is further involved in the reciprocal control of sucrose-driven Tre6P production and/or degradation and its activity is modulated by daily fluctuations in Tre6P levels. End of day (EoD) and end of night (EoN) 20 day-old Arabidopsis thaliana whole rosette samples from control (Col-0), SnRK1α1 overexpressor (SnRK1α1-OE), and SnRK1α partial loss-of-function sesquiα2 mutant (snrk1α1-/- ; snrk1α2+/-), grown under an equinoctial (12:12) photoperiod. Each condition is represented by 3 biological replicates.