Promoter analysis of the sweet potato ADP-glucose pyrophosphorylase gene IbAGP1 in Nicotiana tabacum
The IbAGP1 gene of sweet potato ( Ipomoea batatas ) encodes the sucrose-inducible small subunit of ADP-glucose pyrophosphorylase. Through expression analysis of 5′-truncations and synthetic forms of the IbAGP1 promoter in transgenic tobacco, we show that SURE-Like elements and W-box elements of the promoter contribute to the sucrose inducibility of this gene.
Sweet potato (Ipomoea batatas) contains two genes (IbAGP1 and IbAGP2) encoding the catalytically active small subunits of ADP-glucose pyrophosphorylase, an enzyme with an important role in regulating starch synthesis in higher plants. Previous studies have shown that IbAGP1 is expressed in the storage roots, leaves, and stem tissues of sweet potato, and its transcript is strongly induced by applying sucrose exogenously to detached leaves. To investigate the tissue-specific expression of the IbAGP1 promoter, a series of 5′-truncated promoters extending from bases −1913, −1598, −1298, −1053, −716, and −286 to base +75 were used to drive the expression of the β-glucuronidase reporter gene (GUS) in tobacco plants (Nicotiana tabacum). Histochemical and fluorometric GUS assays showed that (1) GUS expression driven by the longest fragment (1989 bp) of the IbAGP1 promoter was detected in vegetative tissues (roots, stems, leaves), (2) fragments extending to −1053 or beyond retained strong GUS expression in roots, stems, and leaves, whereas further 5′-deletions resulted in considerable reduction in GUS activity, and (3) the series of 5′-truncated promoters responded differently to exogenously applied sucrose. The 1989-bp IbAGP1 promoter contains five sequences (two AATAAAA, one AATAAAAAA, and two AATAAATAAA) that are similar to sucrose-responsive elements (SURE). These SURE-Like sequences are found at nucleotide positions −1273, −1239, −681, −610, and −189. Moreover, putative W-box elements are found at positions −1985, −1434, −750, and −578. Synthetic promoters containing tandem repeats of the 4X SURE-Like or 4X W-box upstream from a minimal CaMV35S promoter-GUS fusion showed significant expression in transgenic tobacco in response to exogenous sucrose. These results show that SURE-Like elements and W-box elements of the IbAGP1 promoter contribute to the sucrose inducibility of this gene.
KeywordsIpomoea batatas IbAGP1 Promoter analysis Nicotiana tabacum GUS expression
We thank Ms. Dayi Wang and Mr. Wenzhao Yan from Sichuan Academy of Agriculture Sciences for their generous help in providing the Nanshu 88. This work was supported by the Natural Science Foundation Project of 31000735, 31371682 and the Fundamental Research Funds for the Central Universities ZYGX2012J109, and startup funds provided by East Carolina University to YQ.
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Conflict of interest
The authors declare that they have no conflict interests.
- Ishiguro S, Nakamura K (1994) Characterization of a cDNA encoding a novel DNA-binding protein, SPF1, that recognizes SP8 sequences in the 5′ upstream regions of genes coding for sporamin and beta-amylase from sweet potato. Mol Gene Genet 244:563–571Google Scholar