ABSTRACT␤-Glucan elicitor (GE), released from the cell wall of the phytopathogenic fungus Phytophthora megasperma by soybean glucanases, causes defense reactions in soybean. A GE-binding protein (GEBP) was purified from the membrane fraction of soybean root cells, and its cDNA was isolated. Expression of the cDNA clone in tobacco suspension cultured cells and in Escherichia coli conferred GE-binding activity to both. An antibody against the recombinant protein was found to inhibit the GE binding with the soybean cotyledon membrane fraction as well as the resulting accumulation of phytoalexin. Immunolocalization assays indicated that the GEBPs are located in the plasma membrane of root cells. These results suggest that the cDNA encodes a GE receptor and may mediate the signaling of the elicitor.Plants defend themselves from infection by invasive phytopathogenic fungi by a combination of constitutive as well as induced defenses such as phytoalexin accumulation; the hypersensitive reaction; and the production of chitinase, glucanase, and polygalacturonase inhibitor (1). Certain defense reactions are elicited by compounds referred to as elicitors, such as oligosaccharides, proteins, and glycoproteins released from fungal and plant cell walls (reviewed in refs. 2-4).

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SummaryHeme activator protein (HAP), also known as nuclear factor Y or CCAAT binding factor (HAP/NF-Y/CBF), has important functions in regulating plant growth, development and stress responses. The expression of rice HAP gene (OsHAP2E) was induced by probenazole (PBZ), a chemical inducer of disease resistance. To characterize the gene, the chimeric gene (OsHAP2E::GUS) engineered to carry the structural gene encoding b-glucuronidase (GUS) driven by the promoter from OsHAP2E was introduced into rice. The transgenic lines of OsHAP2Ein::GUS with the intron showed high GUS activity in the wounds and surrounding tissues. When treated by salicylic acid (SA), isonicotinic acid (INA), abscisic acid (ABA) and hydrogen peroxide (H 2 O 2 ), the lines showed GUS activity exclusively in vascular tissues and mesophyll cells. This activity was enhanced after inoculation with Magnaporthe oryzae or Xanthomonas oryzae pv. oryzae. The OsHAP2E expression level was also induced after inoculation of rice with M. oryzae and X. oryzae pv. oryzae and after treatment with SA, INA, ABA and H 2 O 2, respectively. We further produced transgenic rice overexpressing OsHAP2E. These lines conferred resistance to M. oryzae or X. oryzae pv. oryzae and to salinity and drought. Furthermore, they showed a higher photosynthetic rate and an increased number of tillers. Microarray analysis showed up-regulation of defence-related genes. These results suggest that this gene could contribute to conferring biotic and abiotic resistances and increasing photosynthesis and tiller numbers.

New arrangements of microtubules and actin filaments in coleoptile cells of barley that had been inoculated with either a nonpathogen, Erysiphe pisi, or a pathogen, E. graminis, were observed by cytochemistry and confocal laser scanning microscopy. In uninoculated coleoptile cells, microtubules were oriented almost obliquely or transversely to the long axis of the cells and actin filaments almost obliquely or longitudinally. A thick actin bundle was located beneath approximately 70% of appressoria of E. pisi when the appressoria matured 3–4 h before they attempted penetration. This phenomenon occurred below approximately 30% of appressoria of E. graminis. Microtubules were gathered beneath the appressoria when and after the inoculated fungi induced cytoplasmic aggregation. This phenomenon also occurred more frequently below appressoria of E. pisi than those of E. graminis. Confocal laser scanning microscopy confirmed the localization of microtubules and actin filaments in a cortical region of the coleoptile cell beneath the appressorium. The time-course study revealed that the new arrangement of actin filaments was initiated 3–4 h prior to the fungal penetration attempt, whereas that of microtubules began at the time of initiation of cytoplasmic aggregation. The incidence of cells with newly arranged cytoskeletons was distinctly higher when E. pisi rather than E. graminis was used as inoculum. The possibilities that actin filaments might be involved in sensing the presence of the fungi and that both microtubules and actin filaments might be involved in localized resistance mechanisms are discussed. Key words: microtubule, F-actin, Erysiphe pisi, E. graminis, resistance mechanism.