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.

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The orientation behavior of liquid crystalline solutions of poly (-γ-benzyl-L-glutamate) (PBLG) in chloroform under an electric field was investigated with respect to characteristic electro-optical properties of macromolecules using small angle light scattering and birefringence techniques. The Hv light scattering pattern showed a circular type in the absence of an applied field. This indicates large orientation disorder of optical axes with respect to the molecular cluster axis. When an electric field was applied, the scattering pattern became X type, characterizing the scattering from rodlike textures being a sort of molecular cluster and the scattering lobes were extended to the horizontal direction. This means the preferential orientation of the molecular cluster in the direction of an electric field. In order to analyze the variation of the scattering pattern with increasing electric field, we have carried out theoretical calculations of the basis of a model. In this model system, the orientation distribution function of rods was assumed to be the steady-state orientation distribution function of macromolecules under an electric field which was proposed to investigate electric properties of a dilute solution of rigid macromolecules by O’Konski et al. By using this method, the electric parameters and the optical anisotropy factor of PBLG molecules were separately determined by fitting the experimental birefringence saturation results to the theoretical curve proposed by O’Konski et al. Thus, the steady-state distribution function was determined, and consequently the light scattering patterns were calculated as a function of an electric field strength. The calculated results were found to be rather close to observed ones with a proper choice of parameter associated with the magnitude of the disorder of the optical axes.

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