S601 is the only AA residue phosphorylated by SnRK1.1 at the C-terminal of SLAH3. A, LC–MS/MS was used to analyze the phosphorylated site of SLAH3 C-terminal after phosphorylation by SnRK1.1. S601 of SLAH3 was identified as the only site phosphorylated by SnRK1.1. B, The AA sequence of the C-terminal of SLAH3. The detected phosphorylated peptide is framed and the red-colored pS (S601) is the identified phosphorylation site. C, In vitro kinase assay confirms S601 as the sole phosphorylation site of SLAH3-CT by SnRK1.1. S580A substitution is a control. These assays were performed three times and showed similar results.