Arch Virol (2006) 151: 2111–2122 DOI 10.1007/s00705-006-0802-3 Expression of rice yellow mottle virus coat protein enhances virus infection in transgenic plants N. K. Kouassi 1 , L. Chen 3 , C. Sir´ e 2 , M. Bangratz-Reyser 2 , R. N. Beachy 3 , C. M. Fauquet 3 , and C. Brugidou 2 1 Centre National de Recherche Agronomique (CNRA), Laboratoire Central de Biotechnologies, Abidjan, C ˆ ote d’Ivoire 2 Institut de Recherche pour le D´ eveloppement (IRD), Montpellier, France 3 Donald Danforth Plant Science Center, St. Louis, MO, U.S.A. Received December 7, 2005; accepted May 10, 2006 Published online June 19, 2006 c  Springer-Verlag 2006 Summary. The disease caused by rice yellow mottle virus (RYMV) is a major, economically important constraint to rice production inAfrica. RYMV is mechani- cally transmitted by a variety of agents, including insect vectors. The production of resistant rice varieties would be an important advance in the control of the disease and increase rice production inAfrica. We produced transgenic plants of the Oryza sativa japonica variety, TP309, to express a RYMV coat protein gene (CP) and mutants of the CP under the control of a ubiquitin promoter. Transgenic plants expressing genes that encode wild-type CP (wt.CP), deleted CP (NLS.CP), mRNA of the CP, or antisense CP sequences of the CP gene were characterised. Eighty per cent (80%) of independent transgenic lines analysed contained CP gene sequences. Transgenic plants were challenged with RYMV and produced two types of reactions. Most of the plants expressing antisense sequences of the CP and untranslatable CP mRNA exhibited a delay in virus accumulation of up to a week, and the level of virus accumulation was reduced compared with non-transgenic TP309 plants. Transgenic plants expressing RYMV wild-type CP (wt.CP) and deleted CP (∆NLS.CP) accumulated the highest levels of virus particles. These results suggest that antisense CP and untranslatable CP mRNA induced moderate resistance, whereas transgenic CP enhanced virus infection. Introduction The disease caused by various isolates of Rice yellow mottle virus (RYMV; genus Sobemovirus) is one of the greatest threats to rice production in Africa in both lowland and upland rice systems. The disease can cause yield losses of up to 100% depending upon the variety, the growing stage of the plant at the time of