In silico analysis of cis-elements and identification of transcription factors putatively involved in the regulation of the OAS cluster genes SDI1 and SDI2

A. thaliana sulfur deficiency-induced 1 and sulfur deficiency-induced 2 (SDI1 and SDI2) are involved in partitioning sulfur among metabolite pools during sulfur deficiency and their transcription is strongly induced by this condition. However, little is currently known about the cis- and trans-factors that regulate SDI expression. To identify potential transcription factors and DNA sequence element regulators of SDI expression we performed a comparative in silico analysis of their promoter sequences cataloguing known and potentially new cis-elements. We further screened an arrayed library of Arabidopsis transcription factors (TF) for binding to the SDI1 and SDI2 promoters. In total 14 candidate TF regulators of SDIs were identified with yeast-one-hybrid analyses, of which five bound to both promoters, 4 were specific to SDI1, and 5 were specific SDI2. Direct association between particular cis-elements in these promoter regions and specific TFs was established via electrophoretic mobility shift assays. SLIM1 was shown to bind SURE cis-element(s) in the proximal promoter region of both SDI1 and SDI2. The bZIP core cis-element in the proximal promoter region of SDI2 was shown to be important for bZIP16, bZIP44, and HYH binding. GBF1 was shown to bind the E-box in the proximal promoter region of SDI2. Additionally, we performed a meta-analysis of expression changes of these 14 TF candidates in a variety of conditions that alter SDI expression. These data will allow for more detailed future analysis of the molecular factors required for transcriptional regulation of SDIs under a range of physiological and metabolic conditions, apart from sulfur deficiency.