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RCH1, a Locus in Arabidopsis That Confers Resistance to the Hemibiotrophic Fungal Pathogen Colletotrichum higginsianum

¹Department of Biology, Tokyo Gakugei University, 4-1-1 Nukuikita-machi, Koganei-shi, Tokyo, 184-8501 Japan; ²Kobe University Graduate School of Science and Technology, 1-1 Rokkodai-cho, Nada-ku, Kobe, 657-8501 Japan; ³Laboratory of Plant Molecular Biology, RIKEN Tsukuba Institute, 3-1-1 Koyadai, Tsukuba, 305-0074 Japan; ⁴Plant Mutation Exploration Team, Plant Functional Genomics Research Group, RIKEN Genomic Sciences Center (GSC), RIKEN Yokohama Institute, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, 230-0045 Japan; ⁵Laboratory of Plant Pathology, Graduate School of Agriculture, Kyoto Prefectural University, 1-5 Shimogamonakaragi-cho, Sakyo-ku, Kyoto, 606-8522 Japan; ⁶Laboratory of Environmental Molecular Biology, Graduate School of Integrated Science, Yokohama City University, 1-7-29 Suehiro, Tsurumi, Yokohama, 230-0045 Japan; ⁷Laboratory of Plant Pathology and Genetic Engineering, Faculty of Agriculture, Okayama University, 1-1-1 Tsushimanaka, Okayama, 700-8530 Japan; ⁸Experimental Plant Division, RIKEN Bio Resource Center, 3-1-1 Koyadai, Tsukuba, 305-0074 Japan

When challenged with the crucifer pathogen Colletotrichum higginsianum, Arabidopsis thaliana ecotype Columbia (Col-0) was colonized by the fungus within 2 to 3 days, developing brown necrotic lesions surrounded by a yellow halo. Lesions spread from the inoculation site within 3 to 4 days, and subsequently continued to expand until they covered the entire leaf. Electron microscopy confirmed that C. higginsianum is a hemibiotroph on Arabidopsis, feeding initially on living cells as a biotroph before switching to a necrotrophic mode of growth. A collection of 37 ecotypes of Arabidopsis varied in their responses to infection by C. higginsianum. The ecotype Eil-0 was highly resistant, with symptoms limited to necrotic flecking and with only very limited fungal colonization. Analyses suggested that the hypersensitive response and reactive oxygen species may be important in this defense response. Expression analyses with cDNA microarrays indicated that the defense reaction depends primarily on the jasmonic acid- and ethylene-dependent signaling pathways and, to a lesser extent, on the salicylate-dependent pathway. Crosses between the Eil-0 and Col-0 ecotypes suggested that the resistance in Eil-0 was dominant and was conferred by a single locus, which we named RCH1. RCH1 is the first resistance locus to be identified from Arabidopsis against the hemibiotrophic fungus genus Colletotrichum.