Abstract
Small RNAs regulate various biological process involved in genome stability, development, and adaptive responses to biotic or abiotic stresses. Small RNAs include microRNAs (miRNAs) and small interfering RNAs (siRNAs). MicroRNAs (miRNAs) are regulators of gene expression that affect the transcriptional and post-transcriptional regulation in plants and animals through RNA interference (RNAi). miRNAs are endogenous small RNAs that originate from the processing of non-coding primary miRNA transcripts folding into hairpin-like structures. The mature miRNAs are incorporated into the RNA-induced silencing complex (RISC) and drive the Argonaute (AGO) proteins towards their mRNA targets. siRNAs are generated from a double-stranded RNA (dsRNA) of cellular or exogenous origin. siRNAs are also involved in the adaptive response to biotic or abiotic stresses. The response of plants to hypoxia includes a genome-wide transcription reprogramming. However, little is known about the involvement of RNA signaling in gene regulation under low oxygen availability. Interestingly, miRNAs have been shown to play a role in the responses to hypoxia in animals, and recent evidence suggests that hypoxia modulates the expression of various miRNAs in plant systems. In this review, we describe recent discoveries on the impact of RNAi on plant responses to hypoxic stress in plants.
Highlights
The discovery of microRNAs as regulators of gene expression was a crucial step in understanding the transcriptional and post-transcriptional regulation in plants and animals. miRNAs are small endogenous RNAs with 21–24 nucleotides that originate from the processing of non-coding primary miRNA transcripts folding into hairpin-like structures [1]
The output of the analysis revealed the presence of the hypoxia-responsive promoter element (HRPE) motif above 600 nucleotides upstream of the ATG codon, suggesting that expression of AGO3 could be activated via ERF-transcriptional factors (TFs)
The basis of plant responses to hypoxia involves the activation of the core set of 49 hypoxia-responsive genes (HRGs), which includes genes encoding key enzymes involved in anaerobic fermentation, antioxidant response and sucrose catabolism
Summary
The discovery of microRNAs (miRNAs) as regulators of gene expression was a crucial step in understanding the transcriptional and post-transcriptional regulation in plants and animals. miRNAs are small endogenous RNAs with 21–24 nucleotides that originate from the processing of non-coding primary miRNA (pri-miRNA) transcripts folding into hairpin-like structures [1]. Many miRNAs are highly conserved across plant species and are considered important gene regulators since the majority target transcription factors that participate in common biological processes, such as cellular differentiation, metabolism and hormone signaling. Among the hundreds of genes that show altered expression levels upon hypoxia in Arabidopsis (Arabidopsis thaliana), 49 genes are ubiquitously expressed in all organs and cell types in response to low oxygen [17]. Transcriptomic analyses have highlighted changes in the abundance of mature miRNAs and their precursors in Arabidopsis and corn roots under oxygen deprivation [11,21,22] Most of these miRNAs target genes encoding for transcription factors associated with plant growth and tissue differentiation. Since upregulation of miRNAs reduces the abundance of target mRNAs, hypoxia-upregulated miRNAs may repress the negative regulators of the hypoxic response or slow down plant growth during the stress. We summarize recent work on the regulatory roles of miRNAs in the adaptative responses of plants to low oxygen conditions
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