Emerging Roles of microRNAs in Plant Heavy Metal Tolerance and Homeostasis

Abstract

Heavy metal stress is a major growth-and yield-limiting factor for plants. Heavy metals include essential metals (copper, iron, zinc, and manganese) and non-essential metals (cadmium, mercury, aluminum, arsenic, and lead). Plants use complex mechanisms of gene regulation under heavy metal stress. MicroRNAs are 21-nucleotide non-coding small RNAs as important modulators of gene expression post-transcriptionally. Recently, high-throughput sequencing has led to the identification of an increasing number of heavy-metal-responsive microRNAs in plants. Metal-regulated microRNAs and their target genes are part of a complex regulatory network that controls various biological processes, including heavy metal uptake and transport, protein folding and assembly, metal chelation, scavenging of reactive oxygen species, hormone signaling, and microRNA biogenesis. In this review, we summarize the recent molecular studies that identify heavy-metal-regulated microRNAs and their roles in the regulation of target genes as part of the microRNA-associated regulatory network in response to heavy metal stress in plants.

Morphological Responses and Gene Expression of Grain Amaranth (Amaranthus spp.) Growing under Cd

“…Heavy metal exposure can be manifested on the molecular level by alterations in the expression of a set of genes, commonly termed stress genes or stress-associated genes. Over the past decade, genes involved in the metal stress response have been characterised in a number of plant species [44][45][46]. However, there is little knowledge about the effect of metal stress on the expression of genes in the amaranth genome.…”

Identification of microRNAs and their targets in inflorescences of an Ogura-type cytoplasmic male-sterile line and its maintainer fertile line of turnip (Brassica rapa ssp. rapifera) via high-throughput sequencing and degradome analysis

“…Mature miRNAs are incorporated into the RNA-induced silencing complex to target their respective complementary or nearly complementary mRNAs and then act as inhibitory signals that direct mRNA cleavage or trigger translational repression [27]. MiRNAs emerge as small regulatory molecules of vital plant developmental processes, from vegetative growth to reproduction and stress responses [28][29][30][31][32][33][34].…”

“…Advancements in miRNA arrays and sequencing technology have led to the identification of an increasing number of miRNAs and precursor miRNAs in pollen [35][36][37][38][39][40]. In Arabidopsis, unexpectedly diverse miRNA populations belonging to 33 detected in mature pollen grains, most of which displayed an enriched expression pattern in pollen [37]. There is an increasing amount of evidence confirming that some miRNAs, such as miR159 and miR167, are master modulators of plant male sterility [41][42][43][44].…”

“…High-throughput sequencing and degradome analysis have highlighted the differential expression of miRNAs and their respective targets between CMS and fertile lines in many species [45][46][47][48][49][50][51]. In B. juncea, 47 miRNAs were differentially expressed between CMS and fertile lines, 101 in soybean, 42 in cybrid pummelo (Citrus grandis), and 87 in Chinese cabbage [33,45,48]. Some of these differentially expressed miRNAs were predicted to target transcription factor family proteins or functional proteins with potential roles in male gametophyte development.…”

“…In B . juncea , 47 miRNAs were differentially expressed between CMS and fertile lines, 101 in soybean, 42 in cybrid pummelo ( Citrus grandis ), and 87 in Chinese cabbage [ 33 , 45 , 48 ]. Some of these differentially expressed miRNAs were predicted to target transcription factor family proteins or functional proteins with potential roles in male gametophyte development.…”