Mitsuo Okada

Induction of Resistance against Rice Blast Fungus in Rice Plants Treated with a Potent Elicitor, N-Acetylchitooligosaccharide

The mode of action of a potent elicitor, N-acetylchitooligosaccharide, in rice plants was examined. In intact seedlings, no significant uptake of the elicitor via the roots was observed within 3 h, whereas rapid uptake was observed in excised leaves. Rapid and transient expression of an elicitor-responsive gene, EL2, was induced in the leaves of intact seedlings sprayed with the elicitor or in the roots and leaves of intact seedlings by immersing roots in the elicitor solution. Histochemical analysis indicated that EL2 was expressed in cells exposed to the elicitor of root and leaves. In seedlings treated with the elicitor for 1 d or longer, hyphal growth of rice blast fungus was significantly delayed, and an accumulation of auto-fluorescence around the infection site was observed. Two defense-related genes, PR-1 and PR-10 (PBZ1), were induced in a systemic and local manner by elicitor treatment, in correlation with the induction of resistance against rice blast fungus. N-Acetylchitoheptaose did not inhibit the hyphal growth of the fungi. These results indicate the occurrence of systemic signal transmission from N-acetylchitooligosaccharide in rice plants.

Two purified oligosaccharide elicitors,N-acetylchitohepatose and tetraglucosyl glucitol, derived fromMagnaporthe grisea cell walls, synergistically activate biosynthesis of phytoalexin in suspension-cultured rice cells

Summary Two purified oligosaccharide elicitors generatable from fungal cell walls, N-acetylchitoheptaose and a tetraglucosyl glucitol from rice blast fungus (Magnaporthe grisea), synergistically activated phytoalexin biosynthesis in cultured rice cells. Inhibition experiments for the binding of radiolabeled N-acetylchitooligosaccharide elicitor to the plasma membrane from rice cells indicate that the two elicitors are recognized by different receptors. These results also indicate the presence of a positive interaction between the signal transduction cascade downstream of each elicitor/receptor, which enhances resistance against pathogens.

Identification of a high-affinity binding protein for N-acetylchitooligosaccharide elicitor in theplasma membrane from rice leaf and root cells

Summary Presence of a high-affinity binding protein for N -acetylchitooligosaccharide (fragments of chitin) elicitor in the plasma membrane from rice leaf and root cells was shown by affinity labeling experiments with an 125 I-labeled N -acetylchitooligosaccharide derivative. Binding studies also showed that binding site in the leaf cells has a high affinity to highly elicitor-active, larger chitin fragments but much lower or no affinity to less elicitor-active or elicitor-inactive oligosaccharides. The amount of the binding protein in the leaf cells was slightly smaller than that in the suspension-cultured cells but much larger compared to that in the root cells. These results indicate the possible- involvement of the elicitor binding protein in the perception of the elicitor signal in intact rice plant.

Nod Factor Reception

Gary Stacey, R. Bradley Day, Jonathan Cohn, Mitsuo Okada , Yuki Ito, Serry Koh , Senthil Ramu, Taesik Uhm, Dongjin Kim, Douglas Cook and Naoto Shibuya Center for Legume Research, Department of Microbiology, The University of Tennessee, Knoxville, TN, USA; National Institute of Agrobiological Resources, Tsukuba, Ibaraki 305, Japan; Department of Plant Pathology and Microbiology, Texas A&M University, College Station, TX, USA.