Plant Biotechnology Journal (2005) 3, pp. 187– 202 doi: 10.1111/j.1467-7652.2004.00117.x © 2005 Blackwell Publishing Ltd 187 Blackwell Publishing, Ltd. Expression of the maize proteinase inhibitor (mpi ) gene in rice plants enhances resistance against the striped stem borer ( Chilo suppressalis ): effects on larval growth and insect gut proteinases Laura Vila 1 , Jordi Quilis 1 , Donaldo Meynard 2 , Jean Christophe Breitler 2 , Victoria Marfà 3 , Isabel Murillo 1 , Jean Michel Vassal 2 , Joaquima Messeguer 3 , Emmanuel Guiderdoni 2 and Blanca San Segundo 1, * 1 Departamento de Genética Molecular, Consorci CSIC-IRTA-Laboratori de Genética Molecular Vegetal, Instituto de Biología Molecular de Barcelona, IBMB-CSIC, Jordi Girona 18, 08034 Barcelona, Spain 2 Biotrop and Crop Protection Programmes, CIRAD-Amis, Avenue Agropolis, F-34398 Montpellier Cedex 5, France 3 Departament de Genètica Vegetal, Consorci CSIC-IRTA-Laboratori de Genética Molecular Vegetal, IRTA-Centre de Cabrils, Carretera de Cabrils s/n, Cabrils, 08348 Barcelona, Spain Summary The maize proteinase inhibitor (mpi ) gene was introduced into two elite japonica rice varieties. Both constitutive expression of the mpi gene driven by the maize ubiquitin 1 promoter and wound-inducible expression of the mpi gene driven by its own promoter resulted in the accumulation of MPI protein in the transgenic plants. No effect on plant phenotype was observed in mpi-expressing lines. The stability of transgene expression through successive generations of mpi rice lines (up to the T 4 generation) and the production of functional MPI protein were confirmed. Expression of the mpi gene in rice enhanced resistance to the striped stem borer ( Chilo suppressalis ), one of the most important pests of rice. In addition, transgenic mpi plants were evaluated in terms of their effects on the growth of C. suppressalis larvae and the insect digestive proteolytic system. An important dose-dependent reduction of larval weight of C. suppressalis larvae fed on mpi rice, compared with larvae fed on untransformed rice plants, was observed. Analysis of the digestive proteolytic activity from the gut of C. suppressalis demonstrated that larvae adapted to mpi transgene expression by increasing the complement of digestive proteolytic activity: the serine and cysteine endoproteinases as well as the exopeptidases leucine aminopeptidase and carboxypeptidases A and B. However, the induction of such proteolytic activity did not prevent the deleterious effects of MPI on larval growth. The introduction of the mpi gene into rice plants can thus be considered as a promising strategy to protect rice plants against striped stem borer. Received 2 June 2004; revised 13 September 2004; accepted 6 October 2004 . * Correspondence (fax 34 93 2045904; e-mail bssgmb@cid.csic.es) Keywords: Chilo suppressalis , insect proteinase, maize, proteinase inhibitor, striped stem borer, transgenic rice. Introduction Rice is one of the world’s most important food crops. One of the most devastating pests of rice is the lepidopteran insect striped stem borer (SSB) ( Chilo suppressalis ) (Lepidoptera: Pyralidae). Current strategies for controlling this pest rely on the use of chemical insecticides, which cause public concern about food safety and environmental pollution. Furthermore, C. suppressalis control is difficult using chemical or biological insecticide sprays because the larvae enter the stem shortly after hatching, feed voraciously inside the stem and develop through several larval stages to become pupa. The advent of genetic engineering approaches for insect resistance in crop plants has raised the possibility of achieving high levels of resistance to stem borers in rice. Moreover, efficient gene transfer protocols for the production of fertile transgenic rice plants have been developed (Christou, 1997; Pons et al ., 2000; Sallaud et al ., 2003).