Chitin is a major component of fungal cell walls and serves as a microbe-associated molecular pattern (MAMP) for the detection of various potential pathogens in innate immune systems of both plants and animals. We recently showed that chitin elicitor-binding protein (CEBiP), plasma membrane glycoprotein with LysM motifs, functions as a cell surface receptor for chitin elicitor in rice. The predicted structure of CEBiP does not contain any intracellular domains, suggesting that an additional component(s) is required for signaling through the plasma membrane into the cytoplasm. Here, we identified a receptor-like kinase, designated CERK1, which is essential for chitin elicitor signaling in Arabidopsis. The KO mutants for CERK1 completely lost the ability to respond to the chitin elicitor, including MAPK activation, reactive oxygen species generation, and gene expression. Disease resistance of the KO mutant against an incompatible fungus, Alternaria brassicicola, was partly impaired. Complementation with the WT CERK1 gene showed cerk1 mutations were responsible for the mutant phenotypes. CERK1 is a plasma membrane protein containing three LysM motifs in the extracellular domain and an intracellular Ser/Thr kinase domain with autophosphorylation/myelin basic protein kinase activity, suggesting that CERK1 plays a critical role in fungal MAMP perception in plants.plant immunity ͉ host-pathogen interaction ͉ N-acetylchitooligosaccharide P lants trigger various defense reactions against invading pathogens upon perception of so-called microbe-associated molecular patterns [MAMPs; also known as pathogenassociated molecular patterns (PAMPs)]. MAMP recognition has been implicated to play a major role in the nonhost or basal resistance that makes most plants immune to most potential pathogens (1, 2). In the course of coevolution between hosts and parasites, it seems that pathogens developed various virulence factors to overcome MAMP-mediated defense responses, whereas plants evolved resistance-gene-mediated defense system to detect such factors (3-5). Recent studies also revealed the presence of a striking similarity in the MAMP-mediated immunity between plants and animals (2, 6).Despite the importance of MAMP-mediated immunity in plants, molecular machineries involved in the perception of MAMPs and their signal transduction have been poorly understood. So far, only the receptor molecules for two bacterial MAMPs, flg22 and EF-Tu, have been identified (7,8). Both of these receptors, FLS2 and EFR, are receptor kinases with a leucine-rich repeat in the extracellular domain. However, much less information is available for the perception of fungal MAMPs. Chitin and its fragments, chitin oligosaccharides or N-acetylchitooligosaccharides, are typical fungal MAMPs that trigger various defense responses in both monocots and dicots, indicating the presence of a conserved machinery to perceive these oligosaccharides in a wide range of plant species (9, 10). A recent finding that chitin also induces immune responses in mice (11) suggest...

PAMP (pathogen-associated molecular pattern) recognition plays an important role during the innate immune response in both plants and animals. Lipopolysaccharides (LPS) derived from Gram-negative bacteria are representative of typical PAMP molecules and have been reported to induce defense-related responses, including the suppression of the hypersensitive response, the expression of defense genes and systemic resistance in plants. However, the details regarding the precise molecular mechanisms underlying these cellular responses, such as the molecular machinery involved in the perception and transduction of LPS molecules, remain largely unknown. Furthermore, the biological activities of LPS on plants have so far been reported only in dicots and no information is thus available regarding their functions in monocots. In our current study, we report that LPS preparations for various becteria, including plant pathogens and non-pathogens, can induce defense responses in rice cells, including reactive oxygen generation and defense gene expression. In addition, global analysis of gene expression induced by two PAMPs, LPS and chitin oligosaccharide, also reveals a close correlation between the gene responses induced by these factors. This indicates that there is a convergence of signaling cascades downstream of their corresponding receptors. Furthermore, we show that the defense responses induced by LPS in the rice cells are associated with programmed cell death (PCD), which is a finding that has not been previously reported for the functional role of these molecules in plant cells. Interestingly, PCD induction by the LPS was not detected in cultured Arabidopsis thaliana cells.

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Rice blast caused by an ascomycete fungusMagnaporthe oryzae is the most devastating disease of rice worldwide. Thus understanding of the molecular mechanisms of Magnaporthe-rice interactions is crucial to devise efficient means of disease control. The availability of whole genome sequences of both M. oryzae and rice enables us to analyze their DNA polymorphisms on the genomic scale for the purpose of association genetics as well as for population genomics analysis. Studies on the association between phenotypes-DNA polymorphisms allowed us to isolate three M. oryzae AVR genes, AVR-Pia, AVR-Pii, AVR-Pik/km/kp as well as a rice R-gene, Pia. Population genomics addresses the patterns of DNA polymorphisms to identify the genomic regions under natural selection, a potentially useful tool to isolate the genes involved in plant-pathogen interactions. Recent progress in next-generation sequencing technologies predicts that these approaches would be commonly used to elucidate various host-pathogen interactions.