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Magnaporthe oryzae, the fungus causing rice blast disease, should contend with host innate immunity to develop invasive hyphae (IH) within living host cells. However, molecular strategies to establish the biotrophic interactions are largely unknown. Here, we report the biological function of a M. oryzae-specific gene, equired-for-Focal-IC-ormation 1 (RBF1). RBF1 expression was induced in appressoria and IH only when the fungus was inoculated to living plant tissues. Long-term successive imaging of live cell fluorescence revealed that the expression of RBF1 was upregulated each time the fungus crossed a host cell wall. Like other symplastic effector proteins of the rice blast fungus, Rbf1 accumulated in the biotrophic interfacial complex (BIC) and was translocated into the rice cytoplasm. RBF1-knockout mutants (Δrbf1) were severely deficient in their virulence to rice leaves, but were capable of proliferating in abscisic acid-treated or salicylic acid-deficient rice plants. In rice leaves, Δrbf1 inoculation caused necrosis and induced defense-related gene expression, which led to a higher level of diterpenoid phytoalexin accumulation than the wild-type fungus did. Δrbf1 showed unusual differentiation of IH and dispersal of the normally BIC-focused effectors around the short primary hypha and the first bulbous cell. In the Δrbf1-invaded cells, symplastic effectors were still translocated into rice cells but with a lower efficiency. These data indicate that RBF1 is a virulence gene essential for the focal BIC formation, which is critical for the rice blast fungus to suppress host immune responses. [ABSTRACT FROM AUTHOR]

We show that a rice GRAS family protein, CIGR2, is abonafidetranscriptional activator, and through this function, targets the B-type heat shock protein-encoding geneOsHsf23(Os09g0456800).CIGR2(Os07g0583600) is anN-acetylchitooligosaccharide elicitor-responsive gene whose activity, through the direct transcriptional control ofOsHsf23, is required for mediating hypersensitive cell death activation during pathogen infection. RNAi lines ofCIGR2andOsHsf23similarly exhibited the higher level of granulation in the epidermal cells of leaf sheath inoculated with an avirulent isolate of rice blast fungus. Interestingly, we did not observe altered levels of resistance, suggesting that CIGR2 suppresses excessive cell death in the incompatible interaction with blast fungus via activation ofOsHsf23. N-Acetylchitooligosaccharides-responsiveCIGR2suppresses cell death of rice in cooperation withOsHsf23. [ABSTRACT FROM PUBLISHER]

Chitin is a major molecular pattern for various fungi, and its fragments, chitin oligosaccharides, are known to induce various defense responses in plant cells. A plasma membrane glycoprotein, CEBiP (chitin elicitor binding protein) and a receptor kinase, CERK1 (chitin elicitor receptor kinase) (also known as LysM-RLK1), were identified as critical components for chitin signaling in rice and Arabidopsis, respectively. However, it is not known whether each plant species requires both of these two types of molecules for chitin signaling, nor the relationships between these molecules in membrane signaling. We report here that rice cells require a LysM receptor-like kinase, OsCERK1, in addition to CEBiP, for chitin signaling. Knockdown of OsCERK1 resulted in marked suppression of the defense responses induced by chitin oligosaccharides, indicating that OsCERK1 is essential for chitin signaling in rice. The results of a yeast two-hybrid assay indicated that both CEBiP and OsCERK1 have the potential to form hetero- or homo-oligomers. Immunoprecipitation using a membrane preparation from rice cells treated with chitin oligosaccharides suggested the ligand-induced formation of a receptor complex containing both CEBiP and OsCERK1. Blue native PAGE and chemical cross-linking experiments also suggested that a major portion of CEBiP exists as homo-oligomers even in the absence of chitin oligosaccharides. [ABSTRACT FROM AUTHOR]

Chitin is a major component of fungal cell walls and serves as a molecular pattern for the recognition of potential pathogens in the innate immune systems of both plants and animals. In plants. chitin oligosaccharides have been known to induce various defense responses in a wide range of plant cells including both monocots and dicots. To clarify the molecular machinery involved in the perception and transduction of chitin oligosaccharide elicitor, a high-affinity binding protein for this elicitor was isolated from the plasma membrane of suspension-cultured rice cells. Characterization of the purified protein, CEBiP, as well as the cloning of the corresponding gene revealed that CEBiP is actually a glycoprotein consisting of 328 amino acid residues and glycan chains. CEBiP was predicted to have a short membrane spanning domain at the C terminus. Knockdown of CEBIP gene by RNA interference resulted in the suppression of the elicitor-induced oxidative burst as well as the gene responses, showing that CEBiP plays a key role in the perception and transduction of chitin oligosaccharide elicitor in the rice cells. Structural analysis of CEBiP also indicated the presence of two LysM motifs in the extracellular portion of CEBiP. As the LysM motif has been known to exist in the putative Nod-factor receptor kinases involved in the symbiotic signaling between leguminous plants and rhizobial bacteria, the result indicates the involvement of partially homologous plasma membrane proteins both in defense and symbiotic signaling in plant cells. [ABSTRACT FROM AUTHOR]

Two monomeric lectins, SSA-b-3 and SSA-b-4, were purified from the bark tissue of Japanese elderberry, Sambucus sieboldiana. SDS-PAGE of the purified lectins showed the presence of single bands of 35 and 33 kDa for SSA-b-3 and SSA-b-4, respectively, irrespective of the presence of reducing agent. MS analysis as well as gel filtration of these lectins indicated that they exist mostly as monomeric lectins. Analysis of the N-terminal amino acid sequences of SSA-b-3 and SSA-b-4 yielded an identical sequence, indicating their close structural relationship. Four cDNA clones with extensive homology were obtained from the bark cDNA library and indicated to encode SSA-b-3 or SSA-b-4 from the comparison with the N-terminal sequences of these lectins. These clones were classified into two groups, three for SSA-b-3 and one for SSA-b-4, based on the predicted isoelectric points. The amino acid sequences of the encoded polypeptides were almost identical with the B-chain of a type 2 ribosome-inactivating protein from the same bark tissue, sieboldin-b, except for the absence of a small peptide containing a cystein residue, which is critical for the heteromeric dimerization with an A-subunit. Carbohydrate binding specificity and biological activity of these lectins are also reported. [ABSTRACT FROM PUBLISHER]

We isolated three cDNA clones (pSGJ1, pSGJ2 and pSGJ3) for DnaJ-like proteins of the Japanese willow (Salix gilgiana Seemen). The insert in pSGJ2 included the entire nucleotide sequence of the insert in pSGJ1 that was separated into four parts by three intron-like sequences, and it might correspond to the cDNA for a precursor to the SGJ1 mRNA. The predicted amino acid sequences of SGJ1 (47.5 kDa) and SGJ3 (46.6 kDa) exhibited about 70 to 91% homology to plant cytoplasmic DnaJ-like proteins. SGJ1 was encoded by one or a few genes within the willow genome while SGJ3 was encoded by several genes. Expression of the SGJ1 and SGJ3 genes was compared with that of Hsp70 (SGK1) gene. Constitutive expression of SGJ1, SGJ3 and SGK1 was detected in all organs examined. The SGJ1 mRNA was most abundant in male catkins (inflorescences). High-level expression of SGJ3 and SGK1 was detected in catkins and roots of both male and female plants. The level of the SGJ3 mRNA in the leaves increased about 10-fold after 1 h of heat stress while the expression of SGJ1 mRNA reached a maximum level after 6 h. However, the extent of induction of SGJ1 mRNA was quite low. The levels of SGJ1 and SGJ3 mRNAs in the leaves increased about 6-fold and 2-fold, respectively, after 24 h of treatment with 100 mM NaCl. Thus, the SGJ1 and SGJ3 genes showed differential expression patterns in a variety of organs and in response to different environmental conditions. [ABSTRACT FROM AUTHOR]