We also developed promoter:GUS constructs for AtSBT1.1 and AtPSK4, and found that the gene was expressed at the cut ends of the root segments where callus formation first occurs during shoot regeneration (4 days CIM, Figure 2b ,d). Later, AtSBT1.1 and AtPSK4 continued to be expressed most intensely at sites of callus and regenerative tissue formation, both at the ends and at other wound sites along the length of the root segments (6 days SIM, Figure 2c ,e).