Enhanced resistance to the rice blast fungus Magnaporthe grisea conferred by expression of a cecropin A gene in transgenic rice
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Cecropins are a family of antimicrobial peptides, which constitute an important key component of the immune response in insects. Here, we demonstrate that transgenic rice (Oryza sativa L.) plants expressing the cecropin A gene from the giant silk moth Hyalophora cecropia show enhanced resistance to Magnaporthegrisea, the causal agent of the rice blast disease. Two plant codon-optimized synthetic cecropin A genes, which were designed either to retain the cecropin A peptide in the endoplasmic reticulum, the ER-CecA gene, or to secrete cecropin A to the extracellular space, the Ap-CecA gene, were prepared. Both cecropin A genes were efficiently expressed in transgenic rice. The inhibitory activity of protein extracts prepared from leaves of cecropin A-expressing plants on the in vitro growth of M. grisea indicated that the cecropin A protein produced by the transgenic rice plants was biologically active. Whereas no effect on plant phenotype was observed in ER-CecA plants, most of the rice lines expressing the Ap-CecA gene were non-fertile. Cecropin A rice plants exhibited resistance to rice blast at various levels. Transgene expression of cecropin A genes was not accompanied by an induction of pathogenesis-related (PR) gene expression supporting that the transgene product itself is directly active against the pathogen. Taken together, the results presented in this study suggest that the cecropin A gene, when designed for retention of cecropin A into the endoplasmic reticulum, could be a useful candidate for protection of rice plants against the rice blast fungus M. grisea.
KeywordsAntifungal Cecropin A Oryza Rice blast fungus Transgenic rice
María Coca is a researcher from the Ministerio de Educación y Ciencia (Ramón y Cajal). Gisela Peñas is a recipient of a predoctoral fellowship from the Generalitat de Catalunya. We thank Dr U. Schaffrath for providing us with the PR1a rice cDNA probe. We are grateful to A.B. Moreno and M. Rufat for their collaboration in parts of this work and to P. Fontanet for taking care of the greenhouse plants. We also acknowledge Dr. R. Eritja for synthesis of oligonucleotides and Dr. D. Tharreau for providing us with the M. grisea PR9 isolate. This research was supported by the European Commission (QLRT-CT99-1484, EURICE) and by the Ministerio de Ciencia y Tecnologia (BIO2003-04936-C02). We also thank the “Centre de Referència en Biotecnología” (CeRBa) for substantial support.
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