Engineering Delivery across Plant Barriers: Nano- and Microtechnologies for Plant Bioengineering

Plant bioengineering is moving from proof-of-concept genetic modification toward programmable, spatially controlled, and environmentally responsive intervention in living plants. Yet delivery remains the central bottleneck. Plant tissues impose a nested series of barriers, including the cuticle, stomata, trichomes, cell wall, plasma membrane, apoplast, vascular network, organelle membranes, and rhizosphere microbiome, that restrict the transport and functional deployment of nucleic acids, proteins, sensors, agrochemicals, and living microbes. Conventional approaches such as Agrobacterium-mediated transformation, biolistics, viral vectors, foliar spraying, soil drenching, and trunk injections remain valuable, but they are often limited by genotype dependence, tissue damage, low spatial precision, poor environmental stability, or weak translation across plant species and developmental stages. Nano- and microdelivery technologies offer a delivery-science framework for overcoming these constraints. Nanoscale carriers can interface with cells, organelles, and biomolecules, while microscale devices can access tissues and vascular routes with greater spatial control. Surface coatings, nanosensors, and microbial encapsulation platforms further expand delivery beyond intracellular transport to include retention, monitoring, stress protection, and living cargo deployment. In this review, we organize nano- and microdelivery technologies according to the barriers they address, the cargos they support, the biological scales they access, and the time scales over which they function. We emphasize that delivery success should not be inferred from uptake or fluorescence alone, but should be evaluated through linked evidence of localization, cargo release, biological activity, plant compatibility, microbiome response, environmental fate, and field-relevant performance. Finally, we discuss emerging opportunities in cell- and organelle-targeted delivery, multiplexed cargo administration, hybrid nano–micro systems, synthetic biology, AI-guided material design, and regulatory-ready precision agriculture. By reframing plant bioengineering as a delivery engineering challenge, this review identifies design principles for matching cargo, route, tissue target, biological time scale, and validation strategy to enable more predictable and scalable interventions in living plants.