FIGURE 2.

RNA interference (RNAi) technology in plants. After the molecular and phenotypic characterization of potential target genes (from plants or pathogens), expression cassettes are designed for small RNA accumulation in transgenic plants. Here, three transformation vectors for the expression of three different types of small RNAs are shown: hairpin RNA (hpRNA), artificial microRNA (amiRNA) and target mimicry molecules (miRNA sponges), which are called competitive RNAs (cRNAs) or circular RNAs (circRNAs) and can capture plant or pathogen endogenous miRNAs (emiRNAs). After nuclear transformation, these small RNAs are expressed and processed by the plant cell. The short interfering RNAs (siRNAs) and miRNAs produced combine with the plant RNA-induced silencing complex (RISC), which will promote gene knockdown in the plant (e.g., susceptibility genes) or pathogen (e.g., viruses and virulence genes). For extracellular pathogens (e.g., fungi/oomycetes), the small RNAs produced can be transferred at the site of contact between the plant cell and the pathogen. For more complex multicellular eukaryotes (e.g., insects and nematodes), the delivery of small RNAs occurs mainly through feeding. Additionally, non-transgenic approaches based on nanoencapsulation of dsRNAs or small RNAs can be applied to gene knockdown. PTGS: posttranscriptional gene silencing; vRNA: viral RNA.