Although cytosolic free Ca 2+ mobilization induced by microbe/pathogen-associated molecular patterns is postulated to play a pivotal role in innate immunity in plants, the molecular links between Ca 2+ and downstream defense responses still remain largely unknown. Calcineurin B-like proteins (CBLs) act as Ca 2+ sensors to activate specific protein kinases, CBL-interacting protein kinases (CIPKs). We here identified two CIPKs, OsCIPK14 and OsCIPK15, rapidly induced by microbe-associated molecular patterns, including chitooligosaccharides and xylanase (Trichoderma viride/ethylene-inducing xylanase [TvX/EIX]), in rice (Oryza sativa). Although they are located on different chromosomes, they have over 95% nucleotide sequence identity, including the surrounding genomic region, suggesting that they are duplicated genes. OsCIPK14/15 interacted with several OsCBLs through the FISL/NAF motif in yeast cells and showed the strongest interaction with OsCBL4. The recombinant OsCIPK14/15 proteins showed Mn 2+ -dependent protein kinase activity, which was enhanced both by deletion of their FISL/ NAF motifs and by combination with OsCBL4. OsCIPK14/15-RNAi transgenic cell lines showed reduced sensitivity to TvX/EIX for the induction of a wide range of defense responses, including hypersensitive cell death, mitochondrial dysfunction, phytoalexin biosynthesis, and pathogenesis-related gene expression. On the other hand, TvX/EIX-induced cell death was enhanced in OsCIPK15-overexpressing lines. Our results suggest that OsCIPK14/15 play a crucial role in the microbeassociated molecular pattern-induced defense signaling pathway in rice cultured cells.Calcium ions regulate diverse cellular processes in plants as a ubiquitous internal second messenger, conveying signals received at the cell surface to the inside of the cell through spatial and temporal concentration changes that are decoded by an array of Ca 2+

Cytosolic free Ca(2+) mobilization induced by microbe/pathogen-associated molecular patterns (MAMPs/PAMPs) play key roles in plant innate immunity. However, components involved in Ca(2+) signaling pathways still remain to be identified and possible involvement of the CBL (calcineurin B-like proteins)-CIPK (CBL-interacting protein kinases) system in biotic defense signaling has yet to be clarified. Recently we identified two CIPKs, OsCIPK14 and OsCIPK15, which are rapidly induced by MAMPs, involved in various MAMP-induced immune responses including defense-related gene expression, phytoalexin biosynthesis and hypersensitive cell death. MAMP-induced production of reactive oxygen species as well as cell browning were also suppressed in OsCIPK14/15-RNAi transgenic cell lines. Possible molecular mechanisms and physiological functions of the CIPKs in plant innate immunity are discussed.