Plant miRNA Cross-Kingdom Transfer Targeting Parasitic and Mutualistic Organisms as a Tool to Advance Modern Agriculture

MicroRNAs (miRNAs), defined as small non-coding RNA molecules, are fine regulators of
gene expression. In plants, miRNAs are well-known for regulating processes spanning
from cell development to biotic and abiotic stress responses. Recently, miRNAs have
been investigated for their potential transfer to distantly related organisms where they may
exert regulatory functions in a cross-kingdom fashion. Cross-kingdom miRNA transfer has
been observed in host-pathogen relations as well as symbiotic or mutualistic relations. All
these can have important implications as plant miRNAs can be exploited to inhibit
pathogen development or aid mutualistic relations. Similarly, miRNAs from eukaryotic
organisms can be transferred to plants, thus suppressing host immunity. This two-way
lane could have a significant impact on understanding inter-species relations and, more
importantly, could leverage miRNA-based technologies for agricultural practices.
Additionally, artificial miRNAs (amiRNAs) produced by engineered plants can be
transferred to plant-feeding organisms in order to specifically regulate their crosskingdom
target genes. This minireview provides a brief overview of cross-kingdom
plant miRNA transfer, focusing on parasitic and mutualistic relations that can have an
impact on agricultural practices and discusses some opportunities related to miRNAbased
technologies. Although promising, miRNA cross-kingdom transfer remains a
debated argument. Several mechanistic aspects, such as the availability, transfer, and
uptake of miRNAs, as well as their potential to alter gene expression in a cross-kingdom
manner, remain to be addressed.