Identification of a novel promoter region responsible for the embryo-specific expression of SERK1 in pineapple

Somatic embryogenesis (SE) is a key regeneration process in plant. AcSERK1 is a gene specifically expressed in the early stage of SE in pineapple (Ananas comosus), suggesting that the promoter of SERK1 might contain specific cis-acting element regulating SE. To identify embryonic cell-specific element in the SERK1 promoter, a series of binary plant transformation vectors with GUS (beta-glucuronidase) reporter gene were systematically analyzed by transient gene expression system in wild-type and transgenic pineapple embryogenic callus. Histochemical and quantitative GUS assays demonstrated that the activity of the AcSERK1 upstream regulatory sequence lacking - 921 to -911 or -910 to -880 was significantly reduced in the embryonic callus of the pineapple, and these two regions were needed for the embryonic cell-specific. Besides, a promoter lacking - 943 to -922 was shown to significantly increase GUS activity in embryogenic callus, suggesting repressive elements exist in this region. Our data of stable transformation assays confirmed again the 5' upstream regulatory sequence (-921 to -880) of the AcSERK1 gene is an essential functional region. Our findings lay the basis for better understanding of the molecular mechanisms of AcSERK1 gene in the regulation in early stage of SE.