The sweetpotato GIGANTEA gene promoter is co-regulated by phytohormones and abiotic stresses in Arabidopsis thaliana

GIGANTEA (GI) is known to play significant roles in various molecular pathways. Nevertheless, the underlying mechanism of the transcriptional regulation of GI remains obscure in sweetpotato. In the present study, a 1518-bp promoter sequence was obtained from the Ipomoea batatas GIGANTEA (IbGI) gene, and several potential cis-elements responsive to light, phytohormones and abiotic stresses were identified by in silico analysis. In order to functionally validate the IbGI promoter, the 5' deletion analysis of the promoter was performed by cloning the full-length promoter (D0) and its four deletion fragments, D1 (1235 bp), D2 (896 bp), D3 (549 bp) and D4 (286 bp), upstream of the β-glucuronidase (GUS) reporter gene. Then, these were stably transformed in Arabidopsis plants. All transgenic seedlings exhibited stable GUS activity in the condition of control, but with decreased activity in the condition of most treatments. Interestingly, merely D1 seedlings that contained an abscisic acid responsive cis-element (ABRE-element) had an extremely powerful GUS activity under the treatment of ABA, which implies that fragment spanning nucleotides of -1235 to -896 bp might be a crucial component for the responses of ABA. Eight different types of potential transcriptional regulators of IbGI were isolated by Y1H, including TGA2.2, SPLT1 and GADPH, suggesting the complex interaction mode of protein-DNA on the IbGI promoter. Taken together, these present results help to better understand the transcriptional regulation mechanism of the IbGI gene, and provides an insight into the IbGI promoter, which can be considered as an alternation for breeding transgenic plants.