Regulation of Microbe-Associated Molecular Pattern-Induced Hypersensitive Cell Death, Phytoalexin Production, and Defense Gene Expression by Calcineurin B-Like Protein-Interacting Protein Kinases, OsCIPK14/15, in Rice Cultured Cells    

Abstract

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 microbe-associated molecular pattern-induced defense signaling pathway in rice cultured cells.