Both SRD2 and RID2 are expressed in meristematic tissues, and their transcription is induced after incubation on CIM, indicating that their activities are tightly linked with high proliferative capacities of cells (Ohtani and Sugiyama, 2005; Ohbayashi et al., 2011). These posttranscriptional processes might not be the initial trigger of callus induction, and they are more likely to produce new sets of proteins required for callus formation. Previous proteomic analyses have indeed uncovered dynamic alterations in the nuclear protein profile of Arabidopsis cotyledons undergoing callus induction (Chitteti and Peng, 2007; Chitteti et al., 2008).