Nicotiana tabacum EIL2 directly regulates expression of at least one tobacco gene induced by suphur starvation

Abstract

Sulfur deficiency severely affects plant growth and their agricultural productivity leading to diverse changes in development and metabolisms. Molecular mechanisms regulating gene expression under low sulfur conditions remain largely unknown. AtSLIM1, a member of EIN3-like (EIL) family was reported as a central transcriptional regulator of plant sulfur response, however no direct interaction of this protein with any sulfur responsive promoters was demonstrated. The focus of this study was on analysis of a promoter region of UP9C, a tobacco gene strongly induced by sulfur limitation. Cloning and subsequent examination of this promoter resulted in identification of a 20-nt sequence (UPE-box), present also in the promoters of several Arabidopsis genes, including three out of four homologues of UP9C. The UPE-box consists of two parallel tebs sequences (TEIL binding site) proved to be necessary to bind the transcription factors belonging to EIL family and of a 5-nt conserved sequence at the 3’-end. The yeast one-hybrid analysis resulted in identification of one transcription factor capable of binding to the UPE-box - NtEIL2. The interactions of NtEIL2, and its homolog from Arabidopsis, AtSLIM1, with DNA were affected by mutations within the UPE-box. Transient expression assays in Nicotiana benthamiana have further shown that both factors, NtEIL2 and AtSLIM1, activate UP9C promoter. Interestingly, activation by NtEIL2, but not by AtSLIM1, was dependent on sulfur-deficiency of the plants.