Among plant-specific transcription factors, ethylene response factors (ERFs) comprise one of the largest families. ERFs are unique to the plant kingdom and are considered to have crucial roles in plant response to various biotic and abiotic environmental stresses. Here, we report on the functional analysis of a transcriptional repressor, NtERF3, with regard to cell death associated with a hypersensitive response (HR), a plant-specific resistance reaction against pathogens. Expression of NtERF3 was upregulated during HR induction by Tobacco mosaic virus (TMV) infection in tobacco plants harboring the resistance N gene to TMV. Transient overexpression of NtERF3 by Agrobacterium-mediated gene delivery induced HR-like cell death in tobacco, associated with the production of reactive oxygen species and ion leakage. Deletion of the ERF-associated amphiphilic repression (EAR) motif from NtERF3 resulted in no induction of cell death, while the deletion had no effect on nuclear localization of the proteins. After virus-mediated gene delivery, similar results also were observed in tobacco without the N gene. In addition to NtERF3, other EAR motif-containing ERFs from tobacco, Nicotiana benthamiana and rice also induced cell death when overproduced in tobacco plants. The results suggested that many ERF genes encoding EAR motif-containing proteins might have the ability to induce cell death when overexpressed.

The budding yeast Saccharomyces cerevisiae possesses various defense mechanisms against environmental stresses that generate reactive oxygen species, leading to growth inhibition or cell death. Our recent study showed a novel antioxidative mechanism mediated by nitric oxide (NO) in yeast cells, but the mechanism underlying the oxidative stress tolerance remained unclear. We report here one of the downstream pathways of NO involved in stress-tolerance mechanism in yeast. Our microarray and real-time quantitative PCR analyses revealed that exogenous NO treatment induced the expression of genes responsible for copper metabolism under the control of the transcription factor Mac1, including the CTR1 gene encoding high-affinity copper transporter. Our ChIP analysis also demonstrated that exogenous NO enhances the binding of Mac1 to the promoter region of target genes. Interestingly, we found that NO produced under high-temperature stress conditions increased the transcription level of the CTR1 gene. Furthermore, NO produced during exposure to high temperature also increased intracellular copper content, the activity of Cu,Zn-superoxide dismutase Sod1, and cell viability after exposure to high-temperature in a manner dependent on Mac1. NO did not affect the expression of the MAC1 gene, indicating that NO activates Mac1 through its post-translational modification. Based on the results shown here, we propose a novel NO-mediated antioxidative mechanism that Mac1 activated by NO induces the CTR1 gene, leading to an increase in cellular copper level, and then Cu(I) activates Sod1. This is the first report to unveil the mechanism of NO-dependent antioxidative system in yeast.