Utilization of the Q-System for Synthetic Transcriptional Regulation in Plants

A primary focus of the rapidly growing field of plant synthetic biology is to develop technologies to precisely regulate gene expression and engineer complex genetic circuits into plant chassis. At present, there are few orthogonal tools available for effectively controlling gene expression in plants, with most researchers instead using a limited set of viral elements or truncated native promoters. A powerful repressible—and engineerable—binary system that has been repurposed in a variety of eukaryotic systems is the Q-system from Neurospora crassa. Here, we demonstrate functionality of the Q-system in plants through transient expression in potato (Solanum tuberosum) protoplasts and agroinfiltration in Nicotiana benthamiana leaves. Further, using functional variants of the QF transcriptional activator, it was possible to tune the expression of reporter genes. In addition, complete suppression of the system by the QS suppressor was achieved, along with quinic acid-induced reactivation. As a potential application for plant biosensors, we demonstrated the ability of the Q-system to amplify the signal from a weak promoter, enabling remote detection of a fluorescent reporter that was previously undetectable. Based on the results from this study, the Q-system represents a powerful orthogonal tool for precise control of gene expression in plants, with envisioned applications in metabolic engineering, plant biosensors, and biotic and abiotic stress tolerance.