The plant cell is protected by a complex polysaccharide cell wall composed primarily of cellulose, hemicellulose and pectin. This wall stabilizes a semi-permeable barrier, the plasma membrane (PM) that serves two main roles: (1) transport of essential molecules in and out of the cell, and (2) sensory transduction of environmental stimuli. Considerable progress has been made over the past two decades in understanding plant membrane proteins from a genetic perspective, but complementary tools for physiological, electrophysiological, and biochemical characterization necessary for studying protein functions are lacking. This work promotes a new cell-free, bioelectronic platform that captures the properties of green plant PMs and enables the measurement of plant transporter functions.

Monitoring the flux of metal ions across plant cell membranes through protein transporters embedded within them is a significant challenge today, but is fundamental for assigning function to unknown transporter genes; tackling transporter substrate specificities and modes of regulation; and eventually linking metabolic pathways to cellular compartments, plant growth and development, and bridging the genotype to phenotype gap. Today's technologies are inadequate for a number of reasons, including low throughput and lack of sensitivity, especially for transporters, which have fluxes several orders of magnitude lower than ion channels.

            In this presentation, I will share a new technology that combines planar green plant membranes with transparent, electrically conducting polymer electrodes for the dual-mode (optical or electrical) measurement of plant protein functions. Organic electrochemical transistors (OECT) based on the conductive polymer PEDOT:PSS offer biocompatibility, high-quality electrical signals, and optical monitoring due to the transparency of PEDOT:PSS thin films. We demonstrate here the application of the OECT to the measurement of copper transporter 1 (COPT1), which maintains plant copper homeostasis, but its function has not been wholly characterized. We formed a supported lipid bilayer (SLB) with membranes from transient GFP and GFP-COPT1-transfected Arabidopsis thaliana mesophyll protoplasts on the surface of the OECT. We measure copper flux through COPT1 in a specific and concentration-dependent manner. After data analysis, we obtain kinetic parameters of transport for COPT1 and report on the coupling of COPT1 with another protein, a copper reductase.

This new kind of plant-derived sensor device is amenable to scale up and we anticipate that it can be highly multiplexed for the collection of large data sets on plant transporter systems in a way that has not been possible before. With this capability, such large data sets can be fed into big data science approaches for enabling discoveries and breakthroughs in our understanding of how plants adapt to genetic perturbations, extreme weather conditions, pathogen pressures, and other critical aspects important for flourishing ecosystems.