PtBGL: a cost-effective alternative to GUS reporter with applications in plant imprint dyeing

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 <i>Persicaria tinctoria</i> β-glucosidase (PtBGL) and its natural substrate indican, which is a low-cost indoxyl glucoside extractable from heat-treated indigo plants. When expressed in <i>Arabidopsis thaliana</i> and <i>Nicotiana benthamiana</i>, 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.