Evaluation of dsRNA delivery methods for targeting macrophage migration inhibitory factor MIF in RNAi-based aphid control

Abstract

Macrophage migration inhibitory factors (MIF) are multifunctional proteins regulating major processes in mammals, including activation of innate immune responses. In invertebrates, MIF proteins participate in the modulation of host immune responses when secreted by parasitic organisms, such as aphids. In this study, we assessed the possibility to use MIF genes as targets for RNA interference (RNAi)-based control of the grain aphid Sitobion avenae (Sa) on barley (Hordeum vulgare). When nymphs were fed on artificial diet containing double-stranded (ds)RNAs (SaMIF-dsRNAs) that target sequences of the three MIF genes SaMIF1, SaMIF2 and SaMIF3, they showed higher mortality rates and these rates correlated with reduced MIF transcript levels as compared to the aphids feeding on artificial diet containing a control dsRNA (GFP-dsRNA). Comparison of different feeding strategies showed that the survival of nymphs was not altered when they fed from barley seedlings sprayed with SaMIF-dsRNAs, suggesting they did not effectively take up dsRNA from the sieve tubes of these plants. Furthermore, survival of aphids was also not affected when the nymphs fed on leaves supplied with dsRNA via basal cut ends of barley leaves. Consistent with this finding, the use of sieve-tube-specific YFP-labeled Arabidopsis reporter lines confirmed that fluorescent 21 nt dsRNACy3 supplied via petioles co-localized with xylem structures, but not with phloem tissue. Our results suggest that MIF genes are a potential target for insect control and also imply that application of naked dsRNA to plants for aphid control is inefficient. More efforts should be put into the development of effective dsRNA formulations.

Molecular mechanisms underlying host-induced gene silencing

“…For instance, Biedenkopf et al (2020) reported efficient SIGS of the aphid ( S. avenae ) Shp gene (encoding a structural sheath protein) when applying dsRNA to detached barley leaves. However, Liu et al (2021) reported that the application of naked dsRNA on barley plants was inefficient in silencing different target genes (microphage migration inhibitory factor genes MIF1, MIF2 , and MIF3 ) in the same aphid species, even though nymphs fed an artificial diet containing this dsRNA showed efficient silencing. Furthermore, the authors were unable to detect transport of fluorescently labeled dsRNA into phloem cells, contradicting the findings of Biedenkopf et al (2020) .…”

Analysis of codon usage and allele frequencies reveal the double-edged nature of cross-kingdom RNAi

“…Transgenic barley plants producing double-stranded (ds)RNA exported corresponding sRNAs into the powdery mildew fungus, where they subsequently silenced target genes. Many reports have confirmed that HIGS can mediate strong resistance against target organisms including fungi, oomycetes and insects thereby demonstrating the great agronomic potential of artificial sRNAs (Knip et al 2014; Cai et al 2018b; Liu et al 2020; Šečić and Kogel 2021).…”

A key regulator with a MIF-like domain orchestrates cellular differentiation and virulence in the fungal pathogen Magnaporthe oryzae

“…However, parasitic species have been shown to produce several MIF proteins, some of which are designated for secretion and to modulate the immune responses in the host organism thus facilitating infection (Pastrana et al, 1998; Augustijn et al, 2007; Cho et al, 2011; Miller et al, 2012; Ajonina-Ekoti et al, 2013; Naessens et al, 2015; Zhao et al, 2019). Studies on the mode of action and function of such MIF proteins have mainly been conducted on human and plant parasites such as nematodes, protozoa or aphids (Augustijn et al, 2007; Vermeire et al, 2008, Naessens et al, 2015; Liu et al, 2021).…”