Résumé
The mpi gene encodes a proteinase inhibitor, the MPI (Maize Proteinase Inhibitor) protein, whose expression is induced in response to mechanical wounding and insect feeding in maize plants. MPI was found to be an effective inhibitor of elastase and chymotrypsin activities from the larval midgut of the lepidopteran insect Spodoptera littoralis. In this study, the mpi gene was expressed in rice plants either under the control of the maize-1 ubiquitin promoter or under the control of its own promoter and 3' terminator sequences. MPI was identified in protein extracts from transgenic rice plants by immunoblotting. The stability of transgene expression through successive generations of mpi rice plants was confirmed. Insect feeding experiments revealed that transgenic expression of mpi in rice enhances resistance against striped stem borer (SSB) (Chilo suppressalis Walker), one of the major insect pest of rice. Growth and development of C. suppressalis larvae fed on leaves of rice plants harbouring the mpi gene was significantly retarded, compared to growth of larvae fed in control untransformed leaves. Analysis of proteinase activities present in the gut of C. suppressalis larvae fed on mpi rice plants showed an increase in the total proteolytic activity. The observed overproduction of proteinases is, however, not effective to compensate the inhibitory effect of MPI on the digestive proteolytic activities of C. suppressalis. (Texte intégral)