Exploration of expression activity of subgenomic RNA promoter of coat protein gene from Odontoglossum ringspot virus

The subgenomic mRNA (sgRNA) promoter for coat protein (CP) was isolated from the cDNA infectious clone of Odontoglossum ringspot virus Taiwan strain (ORSV-TW), which is a positive single-stranded RNA virus of the Tobamovirus family. The 5′-end deletion analysis of the 290 nucleotides ORSV CP sgRNA promoter was performed to investigate the promoter activity. A series of different ORSV CP sgRNA promoter deletions were characterized by driving the expression of a fused green fluorescent protein (GFP)-β-glucuronidase (GUS) gene using Agrobacterium-mediated infiltration in Phalaenopsis petals and Nicotiana benthamiana leaves. The results of deletion analysis indicated that the region between 24 nucleotides upstream and 18 nucleotides downstream of translation start codon was sufficient for promoter activity. The activity of this minimal promoter was relatively stronger than other promoters with longer length. A minimal ORSV CP sgRNA promoter was found to accumulate high levels of GFP and GUS, suggesting that this sequence might drive the foreign protein expression in heterologous systems.