RESISTANCE TO TOSPOVIRUSES IN NICOTIANA-BENTHAMIANA TRANSFORMED WITH THE N-GENE OF TOMATO SPOTTED WILT VIRUS - CORRELATION BETWEEN TRANSGENE EXPRESSION AND PROTECTION IN PRIMARY TRANSFORMANTS

Nicotiana benthamiana was transformed with the nucleoprotein (N) gene of an Italian isolate of tomato spotted wilt virus (TSWV), Forty-five T-1 primary transformant lines were analyzed for the expression of N p rotein and for resistance to TSWV and three other tospoviruses: impati ens necrotic spot virus (INSV), groundnut bud necrosis virus (GBNV), a nd groundnut ringspot virus (GRSV). Thirteen of these lines were furth er characterized, Resistance to all TSWV isolates tested was found in two lines, The expression of the transgene (N mRNA) was lower in these resistant lines than in any of the susceptible lines, and the transge ne N protein was either absent or present below detectable levels, The se lines were susceptible to the other tospoviruses tested, but they d eveloped symptoms milder than controls when inoculated with GRSV, Some of the lines producing high levels of N protein showed delays (of 2-3 weeks) in symptom expression with at least one of the TSWV isolates t ested and symptom delay or attenuation with INSV or GRSV (or both), Fr om our results it appears that high expression of TSWV N protein retar ds, in some cases,; disease development by TSWV and INSV. In contrast, the lack of detectable expression of the transgenic N protein, accomp anied by limited production of N transcripts, conferred TSWV-specific resistance.