J. Gen. Plant Pathol. 68 : 8-14 zyxwvuts (2002) zyxwvuts Oat Retrotransposon zyxw OARE-I Is Activated in Both Compatible and Incompatible Interactions with Pathogenic Fungi Yosuke KIMURAl, Yukio TOSA', Shigeyuki BETSUYAKUl, Yukio SASABE2,Reiko TOMITA', Jiro MURAKAMI', Hitoshi NAKAYASHlKll and Shigeyuki MAYAMA'* zyxw ABSTRACT zyxwvu Transcriptional activity of the retrotransposon zyxwvuts OARE-1 was monitored in oat leaves infected with pathogenic fungi. The transcription of OARE-1 was upregulated in both incompatible and compatible interactions between an oat cultivar and Magnaporthe grisea isolates but more extensively in the compatible. OARE-1 was also strongly activated in a Pc2/ Vb-carrying oat line inoculated with Helminthosporium victoriae. The upregulation in the Pc2/ Vb-carrying oat line was reproduced by treatment with victorin C, the major compound of the host-specific toxin produced by the fungus. These results suggest that OARE-1 is responsive to various signals or stresses associated with compatibility and incompatibility. (Received June 11, 2001 ; Accepted September 30, 2001) I " Key words : retrotransposon, oat, zyxwvutsr Avena sativa, Magnaporthe grisea, Helminthosporium victoriae. zyx L INTRODUCTION The T y l -copia type retrotransposon is widely distribut- ed in the plant kingdom and known as a major component in plant gen~mes',~,~~). Most plant retrotransposons seem to be inactive, but some have been reported to be active under specific stages of development and various stress- es3).Tntl and Ttol in tobacco are among the most well characterized3). They are activated by tissue culture, physical stresses such as cutting and wounding, and chemical compounds such as salicylate, methyl jasmonate and elicitors inducing plant defense responses, as well as by infection with . Thus the activa- tion of those retrotransposons seems closely associated with plant defense responses. Furthermore, detailed analyses with Tntl showed that its expression is induced in both compatible and incompatible interactions with pathogen^^*'^"^). We have found a novel retrotransposon in oat and isolated its full-length copy7). This element, designated as OARE-1, was 8665 bp long and a member of the BARE-1 subgroup (DDBJ/EMBL/GenBank Accession No. AB- 061327). The expression of OARE-1 RNA was intensive- ly induced by various abiotic stresses such as wounding, UV light, jasmonic acid and salicylic acid7). OARE-1 was also highly activated by a biotic stress, that is, infection with the crown rust fungus, Puccinia coronata f. sp. auenae7). However, the activation was prominent only in the incompatible interaction7). The crown rust fungus is an obligate parasite and seems to avoid stressing plant tissues in a successful infection. To obtain a general view of the responsiveness of OARE-1 to infection, other types of parasites, such as facultative parasites or facultative saprophytes, should also be tested. In the present study we examined transcriptional re- sponses of OARE-1 against infection with pathogenic microbes other than obligate parasites:*C'The microbes were Helminthosporium uictoriae, which produces a host- specific toxin (HST), victorinZ3), and Magnaporthe grisea, which is the causal agent of blast disease with several host-specific subgroupss). MATERIALS AND METHODS Plant material Plant materials used were Auena satiua L. cv. Shokan 1, and near isogenic lines, IowaX469 and IowaX424, which were developed by Dr. M.D. Simons, USDA, Department of Plant Pathology, Weed and Seed Sciences, Iowa State University, Iowa. Iowa- X469 carries Pc2/ Vb gene and is susceptible to Helminth- sporium uictoriae, while IowaX424 lacks the gene and is resistant to this funguslo).Oat seeds were germinated on damp filter papers in petri dishes for 1 day, then grown in Laboratory of Plant Pathology, Faculty of Agriculture, Kobe University, Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan Agricultural Experiment Station, Okayama Prefectural General Agriculture Center, Sanyo-cho,Okayama 709-0801, Japan * Corresponding author (E-mail : mayama@ kobe-u.ac.jp)