MicroRNA

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By: chandrugcg_77 (103 month(s) ago)

genomics-and-its-applications-in-crop-improvement slides are informative pls send the PPT to my mail ID chandrugcg_77@yahoo.co.in

By: mbboranayaka (103 month(s) ago)

Sir i neeed ur kind help for preperation of my seminar..pls help me by providing this ppt or other materials related to plant microRNAs

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A NEW NETWORK FOR GENE REGULATION MicroRNA and Their impact on plants

What is RNA? : 

What is RNA? Ribonucleic acid Ribonucleotides Types: Coding: messenger RNA (mRNA) Non- coding: Ribosomal RNA (rRNA) Transfer RNA (tRNA) Small nuclear RNA (snRNA) Short interfering RNA (siRNA) Micro RNA (miRNA)

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MicroRNA (miRNA) Small, endogenous, noncoding ss RNAs, ~20-22nt (animals) or 20-24nt (plants) . Many microRNA are conserved, from worm to humans or from ferns to dicots or monocots in plants. Pre- miRNA have a well predicted stem loop hairpin structure. Mature miRNAs can regulate multiple genes.

Cont... : 

Cont... Gene expression regulation. Generally prevents binding of ribosome. Involved in RNA Induced Silencing Complex (RISC) of protein translation.

Discovery of miRNA : 

Discovery of miRNA Discovered by Victor Ambrose, Rosalind Lee and Rhonda Feinbaum in 1993. First miRNA discovered is lin-4 in C.elegans. About 872 miRNA belonging to 42 different families has been identified in 71 different plants (Zhang et.al.2005).

Identification of miRNAs : 

Identification of miRNAs Following approaches are applied for identifying miRNAs Genetic Screening. Direct Cloning after isolation of small RNAs. Computational Strategy. RT-PCR.

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Computational approach : 

Computational approach MIRscan (http://genes.mit.edu/mirscan/). MiRAlign (http://bioinfo.au.tsighua.edu cn/miralign). MiRBase (http://microrna.sanger.ac.uk/).

Real Time (RT-PCR) : 

Real Time (RT-PCR) RT-PCR uses stem loop primer followed by a Tagmann assay to quantify and identify miRNAs. In plants, RT-PCR procedure is carried out for detection of miRNAs.

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The model for biogenesis and post-transcriptional suppression of miRNA

RISC assembly : 

RISC assembly Incorporate a single strand into RISC. contains a member of the Argonaute protein family and miRNA.

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ARGONAUTE Core component. 100KDa protein. Present even in archea & eubacteria. Contain signature PAZ & PIWI domain (Carmell, 2003). PAZ: oligonucleotide binding fold which interact with 3' end of miRNA (Lingel & Sattler, 2004). PIWI: fold similar to RNaseH and can hydrolyze target RNA. (Song et al., 2004). Argonaute PIWI domain

Gene regulation by miRNAs : 

MiRNA-directed translational repression. MiRNA-directed mRNA cleavage. Gene regulation by miRNAs

miRNA-directed mRNA cleavage : 

miRNA-directed mRNA cleavage Perfect or near perfect complementarity. In plants, predominant mechanism. miRNA giude AGO component of RISC to cleave phosphodiester bond of target mRNA within the miRNA binding site. Truncated fragement released & degraded, freeing RISC to recognise & cleave another target mRNA.

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miRNA – mediated mRNA decay

Slide 17: 

(Robert et al; 2010)

Slide 18: 

(Robert et al; 2010)

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Regulatory Role of Plant microRNA

miRNA role in plants : 

miRNA role in plants Developmental regulation Phase transition Floral development Leaf development Vascular development Root development Transcription factors Environmental stress responses

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Phase transition Seed germination Vegetative phase Reproductive phase Flowering initiation Seed production For next generation

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miRNA in Phase Transition miR156 Negatively regulates a group of genes encoding: SQUAMOSA PROMOTER-BINDING PROTEIN- LIKE (SPL) transcription factors, such as SPL3,SPL4, and SPL5 that promote flowering initiation

miR156 over expression prolongs juvenile phase in Arabidopsis : 

miR156 over expression prolongs juvenile phase in Arabidopsis

miR156 targets SPL genes, promoters of phase change : 

miR156 targets SPL genes, promoters of phase change miR156 binding site

miR156 loss-of-function promotes precocious phase change : 

miR156 loss-of-function promotes precocious phase change

Floral development : 

Floral development

ABC Model : 

ABC Model A genes: sepals B + A genes : petals B +C genes: stamens C genes : carpels

ABC Genes : 

ABC Genes In Arabidopsis Class A: APETALA2 (AP2), APETALA1 (AP1) Class B: APETALA3 (AP3), PISTILLATA(PI) Class C: AGAMOUS (AG)

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miR172 also regulates floral architecture. MiR172 inhibits the translation of the AP2 mRNA. the miR172-overproducing transgenic plants exhibit no petals . miR165/166,miR167,miR164 also regulates floral architecture. miR172

miRNA and nutrient signalling : 

miRNA and nutrient signalling Plants take up nutrients from soil. The shoot sends signals to the root to indicate nutrient demands. miRNAs move from shoot to root in phloem and regulate nutrient uptake.

Leaf development : 

Leaf development miR319 has been extensively studied in leaf development. miR166-mediated cleavage of the HD-ZIPIII mRNAs establish the leaf polarity. Determined by a group of class-111 homeodomain leucine zipper(HD-ZIP) transcription factors. Three closely related Arabidopsis HD-ZIP genes are phabulosa (phb), phavoluta (phv), and revoluta (rev). miR165\miR166 have been implicated in the functioning of these transcription factors.

Vascular development : 

Vascular development Transportation of water, nutrient, organic materials, and signaling molecules. Architectural maintenance. ATHB8 and ATHB15 expressed in the vascular tissue and play a major role in the vascular development. miR165/166 and its targets play an important role in vascular development.

Root development : 

Root development miRNA regulation of root development depends on auxin signaling. miR160 regulates Auxin Response Factor 17 (ARF17) through mRNA cleavage. ARF17 regulates a subset of GH3 genes. miR164 also regulate the root formation.

Stress responses : 

Stress responses Two possible modes: SiRNAs that are induced under stress conditions and which repress negative regulators of stress tolerance. SiRNAs whose expression is downregulated by stress to allow the accumulation of positive regulators of stress tolerance.

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miR399 is induced upon phosphate starvation : 

miR399 is induced upon phosphate starvation .

Summary : 

miRNAs inhibit protein synthesis by repressing translation or by bringing about deadenylation and subsequent degradation of mRNA targets . Core components of miRISC includes: AGO family of proteins and GW 182 family of proteins. Plant miRNA have been predicted to regulate a variety of processes, such as development, metabolism and stress responses. Summary

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