Synthetic biosensor circuits generate a frequency-encoded response to phytohormones under a dynamic environment

How do dynamic hormone inputs translate into speed, and precision of response is one of the most challenging questions of science. To approach this question, we constructed minimal synthetic gene circuits capable of responding to plant hormones auxin and salicylic acid (SA). These circuits integrate bacterial multi antibiotic resistance (Mar) repressors that directly detect phytohormones through a ligand-induced conformational switch. The combination of individual circuits in synthetic auxin-SA crosstalk was sufficient to coordinate responses across the cell population with tunable precision and speed in long-term microfluidics experiments. This antagonistic auxin-SA crosstalk retains temporal memory upon extended exposure to hormones and synchronizes the behavior of individual cells with the environmental clock. Our study shows how dynamic hormone inputs can be translated in robust and precise responses with a minimal assembly of bacterial transcriptional repressors, suggesting an alternative regulatory strategy to known plant hormone signaling systems.