Abstract
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 cross-kingdom 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 miRNA-based 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.
Highlights
Plants have evolved sophisticated mechanisms to adapt to environmental changes and to interact with different organisms
Most examples of miRNA cross-kingdom transfer come from plant-pathogen/parasite interactions (Zhang et al, 2016; Wang et al, 2017a; Zhang et al, 2019a)
The cross-kingdom transfer of endogenous plant miRNAs to pathogens or parasites may inhibit their invasive powers while the miRNA transfer from parasitic eukaryotes to plants may suppress the immunity of the host plants
Summary
Plants have evolved sophisticated mechanisms to adapt to environmental changes and to interact with different organisms Many of these strategies are based on the activation and repression of large sets of genes, and miRNAs are important regulator molecules in this scenario. An example of plant miRNA transfer to pathogenic fungi is constituted by miR159 and miR166 from cotton (Gossypium hirsutum), shown to confer resistance to Verticillium dahlia (Zhang et al, 2016) These miRNAs, found in fungal hyphae isolated from infected cotton tissues, were predicted to hit the virulence-related proteins HiC-15 (isotrichodermin C-15 hydroxylase) and Clp-1 (Ca2+-dependent cysteine protease).
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