Topical application of pathogen-specific double-stranded RNA (dsRNA) for virus resistance in plants represents an attractive alternative to transgenic RNA interference (RNAi). However, the instability of naked dsRNA sprayed on plants has been a major challenge towards its practical application. We demonstrate that dsRNA can be loaded on designer, non-toxic, degradable, layered double hydroxide (LDH) clay nanosheets. Once loaded on LDH, the dsRNA does not wash off, shows sustained release and can be detected on sprayed leaves even 30 days after application. We provide evidence for the degradation of LDH, dsRNA uptake in plant cells and silencing of homologous RNA on topical application. Significantly, a single spray of dsRNA loaded on LDH (BioClay) afforded virus protection for at least 20 days when challenged on sprayed and newly emerged unsprayed leaves. This innovation translates nanotechnology developed for delivery of RNAi for human therapeutics to use in crop protection as an environmentally sustainable and easy to adopt topical spray.

Nanotechnology increasingly plays a significant role in vaccine development. As vaccine development orientates toward less immunogenic "minimalist" compositions, formulations that boost antigen effectiveness are increasingly needed. The use of nanoparticles in vaccine formulations allows not only improved antigen stability and immunogenicity, but also targeted delivery and slow release. A number of nanoparticle vaccines varying in composition, size, shape, and surface properties have been approved for human use and the number of candidates is increasing. However, challenges remain due to a lack of fundamental understanding regarding the in vivo behavior of nanoparticles, which can operate as either a delivery system to enhance antigen processing and/or as an immunostimulant adjuvant to activate or enhance immunity. This review provides a broad overview of recent advances in prophylactic nanovaccinology. Types of nanoparticles used are outlined and their interaction with immune cells and the biosystem are discussed. Increased knowledge and fundamental understanding of nanoparticle mechanism of action in both immunostimulatory and delivery modes, and better understanding of in vivo biodistribution and fate, are urgently required, and will accelerate the rational design of nanoparticle-containing vaccines.

In plants, silencing of mRNA can be transmitted from cell to cell and also over longer distances from roots to shoots. To investigate the long-distance mechanism, WT and mutant shoots were grafted onto roots silenced for an mRNA. We show that three genes involved in a chromatin silencing pathway, NRPD1a encoding RNA polymerase IVa, RNA-dependent RNA polymerase 2 (RDR2), and DICER-like 3 (DCL3), are required for reception of long-distance mRNA silencing in the shoot. A mutant representing a fourth gene in the pathway, argonaute4 (ago4), was also partially compromised in the reception of silencing. This pathway produces 24-nt siRNAs and resulted in decapped RNA, a known substrate for amplification of dsRNA by RDR6. Activation of silencing in grafted shoots depended on RDR6, but no 24-nt siRNAs were detected in mutant rdr6 shoots, indicating that RDR6 also plays a role in initial signal perception. After amplification of decapped transcripts, DCL4 and DCL2 act hierarchically as they do in antiviral resistance to produce 21-and 22-nt siRNAs, respectively, and these guide mRNA degradation. Several dcl genotypes were also tested for their capacity to transmit the mobile silencing signal from the rootstock. dcl1-8 and a dcl2 dcl3 dcl4 triple mutant are compromised in micro-RNA and siRNA biogenesis, respectively, but were unaffected in signal transmission.epigenetics ͉ long-distance signaling ͉ RNA interference