title: Brassinosteroid functions in a broad range of disease resistance in tobacco and rice.
abstract: Brassinolide (BL), considered to be the most important brassinosteroid (BR) and playing pivotal roles in the hormonal regulation of plant growth and development, was found to induce disease resistance in plants. To study the potentialities of BL activity on stress responding systems, we analyzed its ability to induce disease resistance in tobacco and rice plants. Wild-type tobacco treated with BL exhibited enhanced resistance to the viral pathogen tobacco mosaic virus (TMV), the bacterial pathogen Pseudomonas syringae pv. tabaci (Pst), and the fungal pathogen Oidium sp. The measurement of salicylic acid (SA) in wild-type plants treated with BL and the pathogen infection assays using NahG transgenic plants indicate that BL-induced resistance does not require SA biosynthesis. BL treatment did not induce either acidic or basic pathogenesis-related (PR) gene expression, suggesting that BL-induced resistance is distinct from systemic acquired resistance (SAR) and wound-inducible disease resistance. Analysis using brassinazole 2001, a specific inhibitor for BR biosynthesis, and the measurement of BRs in TMV-infected tobacco leaves indicate that steroid hormone-mediated disease resistance (BDR) plays part in defense response in tobacco. Simultaneous activation of SAR and BDR by SAR inducers and BL, respectively, exhibited additive protective effects against TMV and Pst, indicating that there is no cross-talk between SAR- and BDR-signaling pathway downstream of BL. In addition to the enhanced resistance to a broad range of diseases in tobacco, BL induced resistance in rice to rice blast and bacterial blight diseases caused by Magnaporthe grisea and Xanthomonas oryzae pv. oryzae, respectively. Our data suggest that BDR functions in the innate immunity system of higher plants including dicotyledonous and monocotyledonous species.
authors.affiliation: Plant Functions Laboratory, RIKEN Institute, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan. nakashi@postman.riken.go.jp
authors.forename: Hideo
authors.initials: H
authors.lastname: Nakashita
authors.forename: Michiko
authors.initials: M
authors.lastname: Yasuda
authors.forename: Takako
authors.initials: T
authors.lastname: Nitta
authors.forename: Tadao
authors.initials: T
authors.lastname: Asami
authors.forename: Shozo
authors.initials: S
authors.lastname: Fujioka
authors.forename: Yuko
authors.initials: Y
authors.lastname: Arai
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Sekimata
authors.forename: Suguru
authors.initials: S
authors.lastname: Takatsuto
authors.forename: Isamu
authors.initials: I
authors.lastname: Yamaguchi
authors.forename: Shigeo
authors.initials: S
authors.lastname: Yoshida
mesh_terms: D060406:Brassinosteroids; D002777:Cholestanols / Q000378:metabolism / Q000494:pharmacology*; D005658:Fungi / Q000502:physiology; D007113:Immunity, Innate / Q000187:drug effects; D012275:Oryza / Q000187:drug effects* / Q000276:immunology; D010935:Plant Diseases / Q000382:microbiology* / Q000821:virology*; D011549:Pseudomonas / Q000502:physiology; D020156:Salicylic Acid / Q000378:metabolism; D013260:Steroids, Heterocyclic / Q000378:metabolism / Q000494:pharmacology*; D013997:Time Factors; D014026:Nicotiana / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism; D014027:Tobacco Mosaic Virus / Q000502:physiology; D014230:Triazoles / Q000494:pharmacology
chemical_list: D060406:Brassinosteroids; D002777:Cholestanols; D013260:Steroids, Heterocyclic; D014230:Triazoles; C412342:brassinazole; D020156:Salicylic Acid; C023623:brassinolide