Abstract

Reporter gene systems are essential tools for monitoring gene expression and transformation efficiency in plant research. The widely used GUS system provides strong, stable, and well-localized signals but requires expensive substrates. Here, we present an alternative based on Persicaria tinctoria β-glucosidase (PtBGL) and its natural substrate indican, which is a low-cost indoxyl glucoside extractable from heat-treated indigo plants. When expressed in Arabidopsis thaliana and Nicotiana benthamiana, PtBGL localizes to plastids and converts indican into a blue indigo pigment visible to the naked eye. Comparative assays in 13 of the 14 tested plant species revealed no detectable background activity from endogenous β-glucosidases at the examined developmental stage. The PtBGL and indican system enables cost-effective transgenic screening, gene expression analysis, and practical applications such as plant-based fabric imprinting.