Functional Analysis of Maize Silk-Specific ZmbZIP25 Promoter.

ZmbZIP25 ( bZIP (basic leucine zipper) transcription factor 25) is a function-unknown protein that belongs to the D group of the bZIP transcription factor family. RNA-seq data showed that the expression of was tissue-specific in maize silks, and this specificity was confirmed by RT-PCR (reverse transcription-polymerase chain reaction). In situ RNA hybridization showed that was expressed exclusively in the xylem of maize silks. A 5' RACE (rapid amplification of cDNA ends) assay identified an adenine residue as the transcription start site of the gene. To characterize this silk-specific promoter, we isolated and analyzed a 2450 bp (from -2083 to +367) and a 2600 bp sequence of (from -2083 to +517, the transcription start site was denoted +1). Stable expression assays in showed that the expression of the reporter gene driven by the 2450 bp 5'-flanking fragment occurred exclusively in the papillae of stigmas. Furthermore, transient expression assays in maize indicated that and expression driven by the 2450 bp 5'-flanking sequences occurred only in maize silks and not in other tissues. However, no or expression was driven by the 2600 bp 5'-flanking sequences in either stable or transient expression assays. A series of deletion analyses of the 2450 bp 5'-flanking sequence was performed in transgenic plants, and probable elements prediction analysis revealed the possible presence of negative regulatory elements within the 161 bp region from -1117 to -957 that were responsible for the specificity of the 5'-flanking sequence.