The Role of MicroRNAs in Defense against Viral Phytopathogens

Abstract

: MicroRNAs have been considered as an endogenous post-transcriptional gene silencing mechanism for transcription regulation. Additionally, reports are indicative of their involvement in plant viral defence. It seems that horizontal miRNA transfer from pathogenic viral and viroid genomes into plants has evolved into counter-defence mechanism(s) against their invasions. miRNAs of a green alga and 16 other higher plant species, with/without endogenous function, were searched for their energetically favorable target sites in the complete genomes of plant-specific invading viruses and viroids. Interestingly, 6524 and 250 potent target sites were found in 759 viral and 16 viroid genomes, respectively. Also, in 5589 viral encoding genes/sequences, 7583 potent target sites from 638 plant invasing viruses were found to be targeted by 1019 miRNAs (belonging to 636 miRNA families). Some miRNA families including miR171, miR156 and miR159 had wide target range in viral genomes; demonstrating possible plant-virus coevolution and at the same time a degree of conservation within different viruses. Such coevolution proposes the existence of immune response mechanism against these sub-genomic organisms, and further suggests adaptive plant-pathogen interactions, something that is known as host specificity. Herein, it was also speculated that some miRNA families such as; miR915, miR899 and miR895 with unknown or non-validated targets in plant genomes are being involved in suppression of invading viruses/viroids.