Identification of Regulatory cis-elements Upstream of AtNPR1 that are Responsive to Probenazole Treatment in Transgenic Tobacco Plants

Abstract

Probenazole (PBZ) is a highly effective chemical inducer of systemic acquired resistance (SAR). We found that the transcript level of NPR1, a key regulator of SAR, was significantly up-regulated upon PBZ treatment in Arabidopsis. To identify cis-elements involved in this response, a series of 5′ deleted fragments in the upstream region of NPR1 were fused to the GUS gene, and the resultant constructs were then introduced into tobacco plants. We have shown that even the shortest of these fragments was able to drive the expression of GUS at a similar level to that of the largest fragment after PBZ treatment. Further mutation analysis within the fragment showed only when both of the two W-boxes present at -128 and -123 were mutated could the responsiveness to PBZ treatment be completely abolished. These results suggest that these two W-boxes are necessary for the full responsiveness of AtNPR1 to PBZ treatment in tobacco plants. This requirement implies that one or more of WRKY transcription factors may play a key role in the positive regulation of PBZ-induced SAR, mediated by AtNPR1. Moreover, the characteristic cross-species responsiveness of the AtNPR1 upstream region to PBZ treatment demonstrates that a conserved regulatory mechanism of PBZ-induced SAR may exist in diverse plant species.