Phosphorylation of Serine 114 of the transcription factor ABSCISIC ACID INSENSITIVE 4 is essential for activity

• MPK3 preferentially phosphorylates Serine 114 of ABI4. Phosphorylated ABI4 is required for the complementation abi4 mutants. acts primarily as a repressor. The transcription factor ABA-INSENSITIVE(ABI)4 has diverse roles in regulating plant growth, including inhibiting germination and reserve mobilization response to ABA high salinity, seedling growth sugars, lateral root repressing light-induced gene expression. activity regulated at multiple levels, expression, protein stability, activation by phosphorylation. Although can be phosphorylated residues MAPKs, we found that S114 preferred site MPK3. To examine possible biological role phosphorylation, transformed - 1 mutant plants with ABI4pro::ABI4 constructs encoding wild type (114S), phosphorylation-null (S114A) or phosphomimetic (S114E) forms Phosphorylation necessary ABA, glucose, salt stress, development, where phenotype could complemented expressing (114S) but not (S114A). Comparison transcriptomes ABA-treated roots different phosphorylation-forms revealed 85 % ABI4-regulated genes whose expression pattern restored are down-regulated was regulation 35 repressed genes, only 17 induced genes. repression requires phosphorylation mainly involved embryo differentiation,