NIM1 overexpression in arabidopsis potentiates plant disease resistance and results in enhanced effectiveness of fungicides

The NIM1 (for noninducible immunity, also known as NPR1) gene is required f or the biological and chemical activation of systemic acquired resistance ( SAR) in Arabidopsis. Overexpression of NIM1 in wild-type plants (hereafter referred to as NIM1 plants or fines) results in varying degrees of resistan ce to different pathogens. Experiments were performed to address the basis of the enhanced disease resistance responses seen in the NIM1 plants. The i ncreased resistance observed in the NIM1 lines correlated with increased NI M1 protein levels and rapid induction of PR1 gene expression, a marker for SAR induction in Arabidopsis, following pathogen inoculation. Levels of sal icylic acid (SA), an endogenous signaling molecule required for SAR inducti on, were not significantly increased compared with wild-type plants. SA was required for the enhanced resistance in NIM1 plants, however, suggesting t hat the effect of NIM1 overexpression is that plants are more responsive to SA or a SA-dependent signal. This hypothesis is supported by the heightene d responsiveness that NIM1 lines exhibited to the SAR-inducing compound ben zo(1,2,3)-thiadiazole-7-car-bothioic add S-methyl ester. Furthermore, the i ncreased efficacy of three fungicides was observed in the NIM1 plants, sugg esting that a combination of transgenic and chemical approaches may lead to effective and durable disease-control strategies.