Small yet mighty - microRNAs in plant-microbe interactions.

Micro RNAs (miRNAs) are short non-coding RNAs of 20-24nt in length mediating RNA silencing, a eukaryotic, sequence-specific repressive gene regulation mechanism. In plants, miRNAs have a pivotal role during fundamental processes such as development, maintenance of genome integrity and abiotic stress responses. They originate from MIRNA genes that are transcribed by RNA polymerase II; MIRNA transcripts form imperfect fold-back structures that are further processed to miRNA duplexes. In Arabidopsis, over 180 MIRNA loci have been identified. Recent evidence shows that miRNAs are substantially implicated in regulating plant immunity. Pathogen attack triggers massive changes in the miRNA transcriptome; many of the altered miRNAs participate in controlling plant hormone pathways. Moreover, microorganisms are known to manipulate silencing pathways to counteract miRNA-mediated defenses. Thus far, miRNAs are believed to likely function as cardinal players in the concert of broad-spectrum disease resistance. Here, we summarize the highlights and latest findings of miRNAs as molecular regulators during plant-microbe interactions.