Signal peptide peptidases are expressed in the shoot apex of rice, localized to the endoplasmic reticulum

Signal peptide peptidase (SPP) is a multi-transmembrane aspartic proteinase involved in regulated intramembrane proteolysis, which is implicated in fundamental life processes such as immunological response, cell signaling, tissue differentiation, and embryogenesis. In this study, we identified two rice SPPs: OsSPP1 and OsSPP2. Green fluorescent protein-fused OsSPP1 and OsSPP2 were localized to the ER in cultured plant cells. In situ hybridization showed that OsSPPs were strongly expressed in vegetative shoot apex, young panicle, developing panicle, and the early developing florets. Undifferentiated cells, which have the potential to differentiate into all of the aerial parts of the plant are presented in the shoot apex. OsSPPs are located in both the undifferentiated cells, and the early differentiated cells at the shoot apex. These results suggest that rice SPPs have an important function in differentiation and development at the shoot apex. The expression of the shoot apex and ER localization is equal to dicot Arabidopsis thaliana, and will have common crucial roles in plant.