In vitro kinase assays. Activity of the purified kinases was determined by in vitro kinase assays using γP32ATP. An equal volume of GST-TaSK1 (71,585 kDa), GST-TaSK2 (71,917 kDa) , GST-BIN2 (69,877 kDa), GST-OsGSK7 (72,174 kDa), GST-TaGSK1 (70.154 kDa), and GST (27,898 kDa) purified fusion proteins was used to test their phosphorylation activity on a myelin basic protein fragment (18,454 kDa). After kinase reaction, samples were loaded on a 12% SDS PAGE gel. After migration, the gel was directly exposed to an X-ray film for either 80 minutes (upper panel) or 24 hours (lower panel). OsGSK7 and BIN2 locus names are respectively RGAP: LOC_Os05g11730 and TAIR: AT4G18710, while the accession of TaGSK1 is GenBank: AF525086.