Abstract
In plants, proper development and response to abiotic and biotic stimuli requires an orchestrated regulation of gene expression. Small RNAs (sRNAs) are key molecules involved in this process, leading to downregulation of their target genes. Two main classes of sRNAs exist, the small interfering RNAs (siRNAs) and microRNAs (miRNAs). The role of the latter class in plant development and physiology is well known, with many examples of how miRNAs directly impact the expression of genes in cells where they are produced, with dramatic consequences to the life of the plant. However, there is an aspect of miRNA biology that is still poorly understood. In some cases, miRNA targeting can lead to the production of secondary siRNAs from its target. These siRNAs, which display a characteristic phased production pattern, can act in cis, reinforcing the initial silencing signal set by the triggering miRNA, or in trans, affecting genes that are unrelated to the initial target. In this review, the mechanisms and implications of this process in the gene regulation mediated by miRNAs will be discussed. This work will also explore techniques for gene silencing in plants that are based on this unique pathway.
Highlights
MicroRNAs are molecules that play pivotal roles in the control of gene expression, and together with small-interfering RNAs they form the two major classes of regulatory small RNAs in plants
This review has discussed some of the crucial aspects related to the production of secondary small interfering RNAs (siRNAs) triggered by miRNA and how this process can add valuable features to the control of gene expression mediated by small RNAs (sRNAs)
Different methods to promote gene silencing in plants that are based on this unique ability of certain miRNAs were discussed, showing that they can be important alternatives to well-established systems, such as artificial miRNA (amiRNA) and hpRNAi
Summary
MicroRNAs (miRNAs) are molecules that play pivotal roles in the control of gene expression, and together with small-interfering RNAs (siRNAs) they form the two major classes of regulatory small RNAs (sRNAs) in plants. Different from classic tasiRNAs, generation of these newly identified secondary siRNAs can be associated with protein-coding genes, and their activity in promoting cleavage of their target in trans is often not shown. These secondary siRNAs are called phased siRNAs (phasiRNAs), and the loci where they come from is referred to as a PHAS gene [20,21]. Different methods to trigger gene downregulation using this silencing mechanism will be discussed
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