Drug Delivery in Plants Using Silk Microneedles

New systems for agrochemical delivery in plants will foster precise agricultural practices and provide new tools to study plants and design crop traits, as standard spray methods suffer from elevated loss and limited access to remote plant tissues. Silk-based microneedles can circumvent these limitations by deploying a known amount of payloads directly in plants' deep tissues. However, plant response to microneedles' application and microneedles' efficacy in deploying physiologically relevant biomolecules are unknown. Here, we show that gene expression associated with Arabidopsis thaliana wounding response decreases within 24 hours post microneedles' application. Additionally, microinjection of gibberellic acid (GA3) in A. thaliana mutant ft-10 provides a more effective and efficient mean than spray to activate GA3 pathways, accelerating bolting, and inhibiting flower formation. Microneedles' efficacy in delivering GA3 is also observed in several monocot and dicot crop species, i.e., tomato (Solanum lycopersicum), lettuce (Lactuca sativa), spinach (Spinacia oleracea), rice (Oryza Sativa), maize (Zea mays), barley (Hordeum vulgare), and soybean (Glycine max). The wide range of plants that can be successfully targeted with microinjectors opens the doors to their use in plant science and agriculture. Overall design: 30-day old ft-10 A. thaliana were injected with GA3-loaded or mock silk microneedles (the mass ratio of silk to GA3 = 60mg : 5.19mg), for a total duration of 0h (no injection), 3h (GA3 microneedle), 24h (GA3 or mock microneedle), and 168h (GA3 microneedle). There are 2-3 biological replicates per timepoint/treatment.