Proteomic analysis of transgenic rice overexpressing a calmodulin calcium sensor reveals its effects on redox signaling and homeostasis

Calmodulin1-1 (Cam1-1) gene in rice (Oryza saliva L.) is highly induced by salt stress and transgenic rice lines overexpressing OsCam1-1 are more salt-tolerant. To identify potential proteins and cellular processes that may be regulated by CaM in rice, a comparative proteomic analysis between wild type and transgenic rice was conducted, which revealed 72 differentially expressed proteins. A Gene Ontology analysis showed that several of these differentially expressed proteins were involved in the response to stimuli and signal transduction. Compared with wild type, the transgenic rice had a higher level of a putative GTPase-activating protein (GAP), a regulatory protein that binds to activated GTP-binding proteins and stimulates their GTPase activity. Real-time RT-PCR analyses verified that GAP transcript levels were higher in all transgenic rice lines than in wild type. A co-expression analysis indicated that GAP was positively and negatively co-expressed with genes encoding peroxidases and glutathione transferases. Under salt stress (150 mM NaCl), guaiacol peroxidase activity was higher in transgenic rice than in wild type. In contrast, compared with wild type, transgenic rice exhibited lower and delayed induction of glutathione transferase activity under salt stress. Under normal conditions, the H2O2 levels were lower in transgenic rice than in wild type. After 24 h of salt stress, H2O2 levels had slightly increased in both wild type and transgenic rice, leading to slightly lower H2O2 levels in transgenic rice than in wild type. Together, these results indicate that OsCam1-1 overexpression may affect redox signaling and homeostasis, resulting in an altered antioxidant system in rice plants under salt stress.