Several cis-elements including a palindrome involved in pollen-specific activity of SBgLR promoter

SBgLR (Solanum tuberosum genomic lysine-rich) is a pollen-specific gene cloned from potato (Solanum tuberosum L.). The region from −269 to −9 (The A of translation start site “ATG” as +1) of the SBgLR promoter was identified as critical for gene specific expression in pollen grains. Sequence analysis indicates a palindromic sequence “TTTCTATTATAATAGAAA” in the −227 to −209 region, in which two pollen-specific motifs TTTCT and AGAAA surround a unique putative TATA box. Moreover, nine putative pollen-specific motifs are located in the region between the TATA box and ATG. We placed the −227 to −9 region (reserving the palindrome) and the −222 to −9 region (breaking the palindrome) downstream of the CaMV35S enhancer, respectively, to construct two fusion promoters. Histochemical assays in transgenic plants demonstrated that the region from −222 to −9 is necessary and sufficient for pollen-specific expression of the uidA gene. However, the region of −227 to −9 is incapable of driving GUS expression in pollen grains and parts of vegetative tissues. A series of 5′ deletions from −269 to −9 of SBgLR promoter were constructed. A transient expression assay indicated that the region from the −227 to −9 suppressed gfp gene expression in pollen, and a positive regulatory element was present in the region of −253 to −227. The function of the palindromic sequence as a repressor inhibiting gene expression in pollen was further confirmed by the mutated promoter, breaking the palindrome by substituting its 3′-flanking five base pairs, which resumes the reporter gene expression in mature pollen.