Identification of a 119-bp Promoter of the Maize Sulfite Oxidase Gene ( ZmSO ) That Confers High-Level Gene Expression and ABA or Drought Inducibility in Transgenic Plants

Drought adversely affects crop growth and yields. The cloning and characterization of drought- or abscisic acid (ABA)-inducible promoters is of great significance for their utilization in the genetic improvement of crop resistance. Our previous studies have shown that maize sulfite oxidase (SO) has a sulfite-oxidizing function and is involved in the drought stress response. However, the promoter of the maize gene has not yet been characterized. In this study, the promoter ( , 1194 bp upstream region of the translation initiation site) was isolated from the maize genome. The in-silico analysis of the promoter identified several -elements responsive to the phytohormone ABA and drought stress such as ABA-responsive element (ABRE) and MYB binding site (MBS), besides a number of core -acting elements, such as TATA-box and CAAT-box. A 5' RACE (rapid amplification of cDNA ends) assay identified an adenine residue as the transcription start site of the . The activity was detected by β-glucuronidase (GUS) staining at nearly all developmental stages and in most plant organs, except for the roots in transgenic . Moreover, its activity was significantly induced by ABA and drought stress. The 5'-deletion mutant analysis of the in tobacco plants revealed that a 119-bp fragment in the (upstream of the transcription start site) is a minimal region, which is required for its high-level expression. Moreover, the minimal was significantly activated by ABA or drought stress in transgenic plants. Further mutant analysis indicated that the MBS element in the minimal region (119 bp upstream of the transcription start site) is responsible for ABA and drought-stress induced expression. These results improve our understanding of the transcriptional regulation mechanism of the gene, and the characterized 119-bp promoter fragment could be an ideal candidate for drought-tolerant gene engineering in both monocot and dicot crops.