Regulates flowering time by modulating the photoperiod pathway. Phosphorylates APRR3. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] A number of isoforms are produced. According to EST sequences. Expressed with a circadian rhythm showing a peak in the evening. Autophosphorylated. Plants display delayed flowering and altered expression of genes involved in the photoperiod flowering pathway, such as ELF4, TOC1, CO and FT. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. WNK subfamily. Was named WNK/'with no lysine(K)' because key residues for catalysis, including the lysine involved in ATP binding, are either not conserved or differ compared to the residues described in other kinase family proteins.