Submitted to: The Plant Cell
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/6/2005
Publication Date: 9/30/2005
Citation: Ivashuta, S., Liu, J., Liu, J., Lohar, D.P., Haridas, S., Bucciarelli, B., VandenBosch, K.A., Vance, C.P., Harrison, M.J., Gantt, J.S. 2005. RNA interference identifies a calcium-dependent protein kinase involved in Medicago truncatula root development. The Plant Cell. 17:2911-2921. Interpretive Summary: Identifying the function of plant genes remains a roadblock to understanding plant growth and development. Although thousands of genes have been sequenced, we know the function for only 50%. One method to identify the function of a gene is to silence (prevent) its expression and then assess how silencing affects plant growth and development. In this research we silenced the expression of a calcium-dependent protein kinase (CDPK) gene in the model legume plant Medicago truncatula. The expression of the CDPK gene was silenced through a novel technology called RNA interference (RNAi). By delivering double-stranded RNA corresponding to CDPK to roots of Medicago, we blocked the expression of the gene in roots. Medicago roots that were silenced in CDPK expression did not form mycorrhizal or nitrogen-fixing root nodule symbioses. Also the roots of CDPK-silenced plants had shorter root hairs, and root cells did not develop normally. These results show that the CDPK gene functions in regulating root growth and development. The work also shows how RNAi technology can be utilized to define the function of plant genes. The findings are important because the research allows scientists to rapidly and efficiently identify the functional role for plant genes.
Technical Abstract: Changes in cellular or sub-cellular Ca2+ concentrations play essential roles in plant development and in the response of plants to their environment. However, the mechanisms through which Ca2+ acts, the downstream signaling components, as well as the relationships among the various Ca2+-dependent processes remain largely unknown. Using a RNA interference-based screen for gene function in Medicago truncatula, we identified a putative Ca2+ sensor that is involved in root development. Silencing MtCDPK1, which is predicted to encode a Ca2+-dependent protein kinase, resulted in significantly reduced root hair and root cell lengths. Inactivation of MtCDPK1 is also associated with significant diminution of both rhizobial and mycorrhizal symbiotic colonization. Additionally, microarray analysis revealed that MtCDPK1 silencing alters cell wall and defense-related gene expression. We propose that MtCDPK1 is a key component of one or more signaling pathways that modulate cell expansion, cell wall synthesis, the defense response, and symbiotic interactions.