Introduction: Viral, bacterial, fungal, and nematode infections can cause significant losses and damage to crops. Treatment options remain limited in agriculture. Accordingly, novel immune activators are required to strengthen plant defense systems and enhance protection against pathogens. Virus-like nanoparticles (VLPs) have been extensively used in developing prophylactic and therapeutic vaccines in animals and humans. However, their potential use in plants is scarce. Hence, they may serve as a promising candidate for novel agricultural solutions and for advancing plant nanotechnology.
Methods: We synthesized protein-based VLPs derived from the bacteriophage Qβ-VLPs encapsulating non-replicative ssRNA. We fluorescently labeled Qβ-VLPs for visualization in Nicotiana benthamiana plants utilizing confocal microscopy. To assess the potential of our nanoparticles to induce an immune response in treated plants, we evaluated the upregulation of the key genes responsible for leaf defense mechanisms against pathogens.
Results: We demonstrate that the fluorescence of the icosahedral 30 nm Qβ-VLPs can be effectively visualized within the intercellular space of (N. benthamiana) one hour post infiltration. Furthermore, infiltration with Qβ-VLPs led to an upregulation in key defense genes (NbPR1a, NbPR5, NbNPR, NbERF1, NbMYC2, and NbLRR2) in treated plants. Using RT-qPCR, a significant increase in the relative expression levels of defense genes was observed, with sustained high levels of NbERF1 and NbLRR2 even after 24 h. Taken together, the data suggest that Qβ-VLPs have a significant capacity to upregulate genes pivotal to leaf defense mechanisms against pathogens in N. benthamiana plants.
Conclusion: We conclude that the dispersal of our protein-based nanoparticles in the intercellular space of N. benthamiana leaves, loaded with ssRNA, initiates a PAMP-triggered immunity. This activation launched a series of signaling cascades, culminating in the enhanced expression of genes associated with various defense mechanisms.
