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Molecular Plant Pathology

Resistance of Transgenic Nicotiana benthamiana Plants to Tomato Spotted Wilt and Impatiens Necrotic Spot Tospoviruses: Evidence of Involvement of the N Protein and N Gene RNA in Resistance. Sheng- Zhi Pang, Department of Plant Pathology, Cornell University, NYSAES, Geneva, NY 14456; Jeffrey H. Bock(2), Carol Gonsalves(3), Jerry L. Slightom(4), and Dennis Gonsalves(5). (2)(4)Molecular Biology Research, Unit 7242, The Upjohn Company, Kalamazoo, MI 49007; (3)(5)Department of Plant Pathology, Cornell University, NYSAES, Geneva, NY 14456. Phytopathology 84:243-249. Accepted for publication 4 November 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-243.

Transgenic Nicotiana benthamiana plants containing the nucleocapsid (N) protein gene of the lettuce isolate of tomato spotted wilt virus (TSWV-BL) have been produced. Analyses of these transgenic plants showed that plants producing small amounts of the N protein were highly resistant to both the homologous isolate and closely related isolates, whereas plants producing large amounts of the N protein possessed moderate levels of protection against both the homologous isolate and two isolates of distantly related impatiens necrotic spot virus (INSV). However, the latter protection was highly dependent on inoculum strength. Despite a delay in symptom appearance in the high expressors, none of the transgenic plants were protected against the more closely related, newly named groundnut ringspot virus originally from Brazil. These results substantiated and extended previous observations in transgenic tobacco. Comparative analyses of transgenic plants expressing either the translatable or the untranslatable N gene showed that protection against the homologous isolate and closely related isolates in plants expressing low levels of the N gene was due to the presence of N gene RNA, whereas protection against the homologous isolate and distantly related INSV isolates in plants expressing high levels of the N gene was due to the accumulation of N protein. Thus, different mechanisms appeared to be involved in protection against infection by tospoviruses that share different levels of N gene sequence identities. Interestingly, both N gene RNA- and N protein-mediated protections are effective against the homologous isolate. These mechanisms cannot operate simultaneously in the same transgenic plant, but they must operate in different plants, because a low level of N gene transcription is required for RNA-mediated protection, whereas a high level of N protein is required for protein-mediated protection. We also compared the nucleotide sequence of the N gene among the test tospovirus isolates, and the information obtained from this comparative analysis was used to develop hypotheses that may account for the two protection patterns.