Here, in a time-course phosphoproteome analysis on Arabidopsis seedlings exposed to control or high ambient temperature, we observed reduced levels of diverse proteins over time, which could be in part due to transcription, translation and/or degradation. In addition, we observed differential phosphorylation of the LRR F-box protein SLOMO MOTION (SLOMO) at two serine residues. We demonstrated that SLOMO is a negative regulator of hypocotyl growth, and protein-protein interaction studies revealed possible interactors of SLOMO.