Small Silencing RNAs in Plants Are Mobile and Direct Epigenetic Modification in Recipient Cells

Abstract

A silencing signal in plants with an RNA specificity determinant moves through plasmodesmata and the phloem. To identify the mobile RNA, we grafted Arabidopsis thaliana shoots to roots that would be a recipient for the silencing signal. Using mutants that block small RNA (sRNA) biogenesis in either source or recipient tissue, we found that transgene-derived sRNA as well as a substantial proportion of the endogenous sRNA had moved across the graft union, and we provide evidence that 24-nucleotide mobile sRNAs direct epigenetic modifications in the genome of the recipient cells. Mobile sRNA thus represents a mechanism for transmitting the specification of epigenetic modification and could affect genome defense and responses to external stimuli that have persistent effects in plants.

Mobile small RNAs and their role in regulating cytosine methylation of DNA

“…39 Thousands of endogenously-derived sRNAs move shoot-toroot, but via the phloem and following source-sink relationships. 44 Twenty-four nt sRNAs are the predominant shoot-root mobile species, though other sizes move also. 44,45 These direct methylation at TEs from families that are typically short and located near genes as well as at transgenes.…”

“…44 Twenty-four nt sRNAs are the predominant shoot-root mobile species, though other sizes move also. 44,45 These direct methylation at TEs from families that are typically short and located near genes as well as at transgenes. 44,46 They are able to enter root meristem tissues and direct silencing of transgenes therein.…”

“…44,46 They are able to enter root meristem tissues and direct silencing of transgenes therein. 44,45 They also transmit methylation variants from shoots of one A. thaliana accession to roots of another. 46 The mechanism by which sRNAs are transmitted within the phloem is not fully described, but likely involves binding by proteins found in the photosynthate.…”

“…44,45 These direct methylation at TEs from families that are typically short and located near genes as well as at transgenes. 44,46 They are able to enter root meristem tissues and direct silencing of transgenes therein. 44,45 They also transmit methylation variants from shoots of one A. thaliana accession to roots of another.…”

Ingested plant miRNAs regulate gene expression in animals

“…Under these circumstances, small RNAs act in defense mechanisms by directing the destruction of the invader. Importantly, exogenous small RNAs and some endogenous small RNAs are mobile within certain organisms [5]. Moreover, exogenous small RNAs can be amplified during the defense mechanisms, allowing the spreading of RNA silencing from the cell where it is activated to the rest of the organism [6].…”