Table 1. Examples of trans-kingdom RNA-mediated signal transfer.

Species				Experimental evidence	Ref.
From	K	To	K
Homo sapiens	A	Plasmodium falciparum	C	Detection of miRNA and annealing to mRNA in target-species	[16]
Trypanosoma cruzi	Pr	Homo sapiens	A	Detection of sRNAs in extracellular vesicles. No direct evidence for sRNA effect, but vesicles induce effect.	[14]
Botrytis cinerea	F	Arabidopsis thaliana, Solanum lycopersicum	P	Detection of sRNAs and down-regulation of their targets in the host species. Hijack of RNAi machinery by fungal sRNAs.	[23]
Triticum aestivum	P	Puccinia triticina	F	RNA produced from RNA virus in planta leads to gene down-regulation in target species	[62]
Hordeum vulgare	P	Blumeria graminis	F	Hairpin expression in planta leads to gene down-regulation in target species	[18]
Medicago truncatula	P	Glomus intraradices	F	Hairpin expression in planta leads to gene down-regulation in target species	[21]
Musa paradisiaca	P	Fusarium oxysporum	F	Phenotype of fungus grown in vitro on medium containing sRNA. Hairpin expression in planta leads to gene down-regulation in target species	[20]
Arabidopsis thaliana	P	Fusarium graminearum	F	Hairpin expression in planta leads to gene down-regulation in target species and suppresses fungal growth	[19]
Nicotiana tabacum	P	Phytophtora capsici	C	Hairpin expression in planta leads to gene down-regulation in target species	[28]
Glycine max	P	Meloidogyne incognita	A	Hairpin expression in planta leads to gene down-regulation in target species	[22]
Arabidopsis thaliana, Nicothiana benthamiana	P	Helicoverpa armigera	A	Hairpin expression in planta leads to gene down-regulation in target species	[24]
Zea mays	P	Diabrotica virgifera and other coleopteran spp.	A	Hairpin expression in planta leads to gene down-regulation in target species	[30]
Arabidopsis thaliana	P	Myzus persicae	A	Hairpin expression in planta leads to gene down-regulation in target species	[63]
Escherichia coli	B	Caenorhabditis elegans	A	Bacterial ncRNAs down-regulate genes and alter nematode behavior	[17]

The “From” and “To” columns indicate the direction of the reported signals. The “K” column shows the kingdom in which the organisms are classified. Although more advanced classifications of the tree of life have been proposed, we chose to use the six kingdom system proposed by Cavalier-Smith in 1998 [64]. P, Planta; A, Animalia; F, Fungi; B, Bacteria; C, Chromists; Pr, Protists.