Identification of a Tobacco mosaic virus elicitor-responsive sequence in the resistance gene N

The N gene of Nicotiana tabacum cv. Samsun NN is a resistance gene for Tobacco mosaic virus. The transcription of the gene increases immediately after virus infection or transient expression of the elicitor p50, a helicase domain of the virus 126/180 K replicases. In this study, we cloned the upstream sequences of the N gene from Samsun NN and fused them to the GFP reporter gene for promoter assays. Agrobacterium-mediated transient gene expression in N. tabacum cv. Samsun nn lacking the N gene allowed us to evaluate promoter activity with or without the expression of p50 and/or N. Individual expression of p50 or N specifically stimulated the N promoter, although the stimulation by N was less prominent than that of p50. The coexpression of p50 and N resulted in higher stimulation of the N promoter than the individual expression. Through deletion and gain-of-function analyses of the upstream region, we identified a 20-bp elicitor-responsive sequence that was essential and sufficient for promoter stimulation by p50 and N. Based on these data, we discuss the possibility that the virus elicitor and N may mediate cooperatively the stimulation of the N promoter upon virus infection.