MicroRNA (miRNA) are small, single-stranded, non-coding RNA molecules containing 21 to 23 nucleotides. Found in plants, animals and some viruses, miRNAs are involved in RNA silencing and post-transcriptional regulation of gene expression. miRNAs base-pair to complementary sequences in mRNA molecules, then silence said mRNA molecules by one or more of the following processes:
- Cleavage of the mRNA strand into two pieces,
- Destabilization of the mRNA by shortening its poly(A) tail, or
- Reducing translation of the mRNA into proteins.
Florigens are proteins capable of inducing flowering time in angiosperms. The prototypical florigen is encoded by the FT gene and its orthologs in Arabidopsis and other plants. Florigens are produced in the leaves, and act in the shoot apical meristem of buds and growing tips.
RNA silencing or RNA interference refers to a family of gene silencing effects by which gene expression is negatively regulated by non-coding RNAs such as microRNAs. RNA silencing may also be defined as sequence-specific regulation of gene expression triggered by double-stranded RNA (dsRNA). RNA silencing mechanisms are conserved among most eukaryotes. The most common and well-studied example is RNA interference (RNAi), in which endogenously expressed microRNA (miRNA) or exogenously derived small interfering RNA (siRNA) induces the degradation of complementary messenger RNA. Other classes of small RNA have been identified, including piwi-interacting RNA (piRNA) and its subspecies repeat associated small interfering RNA (rasiRNA).
The miR-129 microRNA precursor is a small non-coding RNA molecule that regulates gene expression. This microRNA was first experimentally characterised in mouse and homologues have since been discovered in several other species, such as humans, rats and zebrafish. The mature sequence is excised by the Dicer enzyme from the 5' arm of the hairpin. It was elucidated by Calin et al. that miR-129-1 is located in a fragile site region of the human genome near a specific site, FRA7H in chromosome 7q32, which is a site commonly deleted in many cancers. miR-129-2 is located in 11p11.2.
In molecular biology, mir-160 is a microRNA that has been predicted or experimentally confirmed in a range of plant species including Arabidopsis thaliana and Oryza sativa (rice). miR-160 is predicted to bind complementary sites in the untranslated regions of auxin response factor genes to regulate their expression. The hairpin precursors are predicted based on base pairing and cross-species conservation; their extents are not known. In this case, the mature sequence is excised from the 5' arm of the hairpin.
The plant mir-166 microRNA precursor is a small non-coding RNA gene. This microRNA (miRNA) has now been predicted or experimentally confirmed in a wide range of plant species. microRNAs are transcribed as ~70 nucleotide precursors and subsequently processed by the Dicer enzyme to give a ~22 nucleotide product. In this case the mature sequence comes from the 3' arm of the precursor, and both Arabidopsis thaliana and rice genomes contain a number of related miRNA precursors which give rise to almost identical mature sequences. The mature products are thought to have regulatory roles through complementarity to messenger RNA.
The mir-172 microRNA is thought to target mRNAs coding for APETALA2-like transcription factors. It has been verified experimentally in the model plant, Arabidopsis thaliana. The mature sequence is excised from the 3' arm of the hairpin.
miR-196 is a non-coding RNA called a microRNA that has been shown to be expressed in humans and mice. miR-196 appears to be a vertebrate specific microRNA and has now been predicted or experimentally confirmed in a wide range of vertebrate species. In many species the miRNA appears to be expressed from intergenic regions in HOX gene clusters. The hairpin precursors are predicted based on base pairing and cross-species conservation—their extents are not known. In this case the mature sequence is excised from the 5' arm of the hairpin.
mir-395 is a non-coding RNA called a microRNA that was identified in both Arabidopsis thaliana and Oryza sativa computationally and was later experimentally verified. mir-395 is thought to target mRNAs coding for ATP sulphurylases. The mature sequence is excised from the 3' arm of the hairpin.
mir-399 is a microRNA that was identified in both Arabidopsis thaliana and Oryza sativa computationally and was later experimentally verified. mir-399 is thought to target mRNAs coding for a phosphate transporter. The mature sequence is excised from the 3' arm of the hairpin. There are multiple copies of MIR399 in each plant genome, for example A. thaliana contains six microRNA precursors that all give rise to an almost identical mature miR-399 sequence.
This family represents the microRNA (miRNA) precursor mir-7. This miRNA has been predicted or experimentally confirmed in a wide range of species. miRNAs are transcribed as ~70 nucleotide precursors and subsequently processed by the Dicer enzyme to give a ~22 nucleotide product. In this case the mature sequence comes from the 5' arm of the precursor. The extents of the hairpin precursors are not generally known and are estimated based on hairpin prediction. The involvement of Dicer in miRNA processing suggests a relationship with the phenomenon of RNA interference.
Trans-acting siRNA are a class of small interfering RNA (siRNA) that repress gene expression through post-transcriptional gene silencing in land plants. Precursor transcripts from TAS loci are polyadenylated and converted to double-stranded RNA, and are then processed into 21-nucleotide-long RNA duplexes with overhangs. These segments are incorporated into an RNA-induced silencing complex (RISC) and direct the sequence-specific cleavage of target mRNA. Ta-siRNAs are classified as siRNA because they arise from double-stranded RNA (dsRNA).
The SQUAMOSA promoter binding protein-like family of transcription factors are defined by a plant-specific DNA-binding domain. The founding member of the family was identified based on its specific in vitro binding to the promoter of the snapdragon SQUAMOSA gene. SBP proteins are thought to be transcriptional activators.
Vegetative phase change is the juvenile-to-adult transition in plants. This transition is distinct from the reproductive transition and is most prolonged and pronounced in woody species. Manipulating phase change may be an important avenue for plant improvement.
In molecular biology mir-390 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms.
In molecular biology mir-396 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms.
In molecular biology mir-408 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms.
In molecular biology mir-398 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms.
LUX or Phytoclock1 (PCL1) is a gene that codes for LUX ARRHYTHMO, a protein necessary for circadian rhythms in Arabidopsis thaliana. LUX protein associates with Early Flowering 3 (ELF3) and Early Flowering 4 (ELF4) to form the Evening Complex (EC), a core component of the Arabidopsis repressilator model of the plant circadian clock. The LUX protein functions as a transcription factor that negatively regulates Pseudo-Response Regulator 9 (PRR9), a core gene of the Midday Complex, another component of the Arabidopsis repressilator model. LUX is also associated with circadian control of hypocotyl growth factor genes PHYTOCHROME INTERACTING FACTOR 4 (PIF4) and PHYTOCHROME INTERACTING FACTOR 5 (PIF5).
RNA-directed DNA methylation (RdDM) is a biological process in which non-coding RNA molecules direct the addition of DNA methylation to specific DNA sequences. The RdDM pathway is unique to plants, although other mechanisms of RNA-directed chromatin modification have also been described in fungi and animals. To date, the RdDM pathway is best characterized within angiosperms, and particularly within the model plant Arabidopsis thaliana. However, conserved RdDM pathway components and associated small RNAs (sRNAs) have also been found in other groups of plants, such as gymnosperms and ferns. The RdDM pathway closely resembles other sRNA pathways, particularly the highly conserved RNAi pathway found in fungi, plants, and animals. Both the RdDM and RNAi pathways produce sRNAs and involve conserved Argonaute, Dicer and RNA-dependent RNA polymerase proteins.
