Molecular Analysis Of SAM & RAM
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Transcript of Molecular Analysis Of SAM & RAM
TILAK. I SPG14AGR6074
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Introduction
Meristem
SAM
RAM
Conclusions
contentsMolecular Analysis
Of SAM & RAM
INTRODUCTION
• Plant Tissues fall into two large categories:
Meristematic.
Permanent (Non-Meristematic)
Term”meristem” was first used in
1858 by Carl Wilh. V. Nagell
Greek word ”merizein ” to divide.
Contains undifferentiated cells (meristematic cells).
Found in zones of the plant where growth can take place.
Epidermal (L1) Subepidermal (L2) Tunica.
(L3) Inner most layer corpus
meristem
Tunica determine the physical characteristics of the leaf edge and margin.
Positional information (auxin
accumulation) precedes leaf initiation
Auxin accumulation precedes leaf initiation
Indole-3-acetic acid (IAA) a naturally occurring auxin
A boundary forms by the action of
mutually antagonistic genes
ARP
KNOX1
KNOX1 genes, expressed in the
meristem,
ARP genes, expressed in the leaf
primordia, are mutually repressive,
and help establish a separate identity
for the emerging leaf primordium
Apical meristems(Growing tip)
• Found in the buds and growing tips of roots in plants.
1) Growth of new cells in young seedlings at the tips of roots and shoots .
2) An active apical meristem lays down a growing root or shoot behind itself.
Apical Meristems
• In plants belonging to the MONOCOT , apical meristems are located ONLY in the root tips.
• REVOLUTA gene is necessary for Apical meristemdevelopment
STM and CUC1 Expression (Apical Meristem)
• CUC1 redundantly required for embryonic apical meristemformation, cotyledon separation and expression of STM..
Cup shaped cotyledon
Intercalary Meristems
• Plants in the MONOCOT class have special meristems called intercalary meristems.
• Lateral meristems
• Cause SECONDARY GROWTH.
• meristems located in the shoot and root tips, plants in the DICOT class have lateral meristems.
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(Jean et al.,2007) 12
Shoot apical meristems
• 14 days later, leaves have developed (right).
Shoot apical meristem - Importance
• Center of postembryonic growth & development
• Source of all primary meristems
– Protoderm, ground meristem & procambium
• Source of
– Leaves
– Branches
– Tendrils
– Thorns
• Self-renewing mass of cells stem cells
• Balance cell division and cell differentiation
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The shoot apical meristem consists of 4 distinct cell groups:
Stem cells.
The immediate daughter cells of the stem cells.
A subjacent organising centre.
Founder cells for organ initiation in surrounding regions.
are maintained by a complex signalling pathway
Shoot apical meristem organization
L1 = tunica
L2 = tunica
Peripheral Zone
Pith or Rib Meristem
Central Zone
Stem Cells
Organizing Center
L3 = corpus
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Development involves positional
informationAuxin gradients are regulated by auxintransporters)
Movement of a signal away from a source
… selective destruction of a signal by miRNAcleavage of mRNAs)
REVOLUTA gene is necessary for Apical meristem development
Development involves boundaries
Shoot apical meristem
Boundaries form between the shoot apical meristem and leaf primordia, and between the upper and lower surfaces of the leaf
Patterning of cells in the epidermis also involves production of inhibitory signals
Genes necessary for (SAM)
SHOOT- MERISTEMLESS (STM) Late globular embryo.
WUSCHEL (WUS) Early Globular stage @ cells below the stem cells
CLAVATA1 (CLV1)
CLAVATA3 (CLV3)
• SAM becomes distinquishable at torpedo stage.
Early Heart – shaped embryo Size ,Cell divisionSignalling
Clavata’s Molecular Mechanism
• CLAVATA 1, 2 and 3 mutants have identical phenotypes of enlarged meristems
• CLAVATA3 protein acts as a signal molecule.
• The CLAVATA receptor is a leucine rich repeat (lrr) serine/threonine kinasereceptor.
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CLAVATA GENE CharacteristicsCLV1 – Extracellular polypeptide: 96 amino acids
Restricted to L1, L2 of SAM Central ZoneCLV2 – Membrane-bound protein receptor with a protein-binding motifCLV3 – Membrane-bound protein receptor with a protein-binding motif and
Restricted to L1, L2 of SAM Central ZoneKinase activity… signaling… Kinase cascadeInhibitory to WUS expression
Shoot Development : GeneticsCLAVATA gene mechanism
Protein-binding motif
Signal transduction pathway
WUSCHEL(WUS) molecular mechanism
• wus mutants result in1. Early termination of SAM wus defective in maintaining SAM
2. Aberrant SAM organization wus defective in maintaining SAM integrity
WUS function:
1. WUS Protein product is a homeodomaintranscription factor
2. Gene regulation
3. Positional influence of once cell type by another
Localization of WUS geneproduct in organizingcenter (OC) of shoot
L1L2L3
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Shoot Development : GeneticsWUSCHEL gene phenotype
Wild Type
wus mutant
Wild type SAM
wus SAM
mutants but it fails to develop
Gene Interaction: WUSCHEL and CLAVATA Initiation of an Organizing Center in the shoot apical meristem
1. OC precursor lineage established in 4 subepidermal cells of 16 cell proembryo as indicated by expression of WUS (red)
2. Stem cells of Central Zone induced by heart stage as indicated by expression of CLV3 gene (blue)
CLV3 expression
WUS expression ( Gene Regulation )
( Cell division )
mRNA Expression Domains and gene interactionfor CLV1 CLV3 and WUS
clv mutant
Wild type
Wild-type mRNA expression domains illustrate location of gene expression.
1. WUS – under stem cells of Central Zone
2. CLV3 – stem cells of Central Zone above OC (produces extracellular protein)
3. CLV1 – Organizing Center (OC) & vicinity (produces membrane-bound protein)
wus mutant
OverexpressedWUS mutant
A feedback look between WUS and CLV exists because:
1. Expansion of the WUS expression domain in a clvmutant suggests a feedback loop between the twogenes.
2. wus mutants have downregulated (smaller) CLV3expression domain.
3. WUS overexpressed mutants have a broader CLV3expression domain.
Normal SAM
clavata SAM
Shoot Development II: GeneticsCLAVATA gene phenotype
1. CLV localization in Central Zone of SAM
2. Mutant phenotype: Huge apical meristems CLV wild type restricts stem cell accumulation
CLV localization in Central Zone of SAM
STM molecular mechanism
– Stem cells of Central Zone andperipheral Zone.
– Encodes homeodomain proteinKNOTTED Class
– Transcription factor
– Prevents prematuredifferentiation of cells fromPeripheral Zone.
Wild type Stm mutant
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Some Genes Involved in Root-Shoot Formation
Both shoot and root meristems are apical meristems, but are independently controlled
-Shootmeristemless (STM) is necessary for shoot formation, but not root development
STM wild type
stm mutant
-STM encodes a transcription factorwith homeobox region Cotyledons not mature leaves
are shown
Laux, T., et al. Plant Cell 2004;16:S190-S202
Gene Expression in the Apical Embryo DomainWUSCHEL (WUS), CLAVATA (CLV) AND SHOOT MERISTEMLESS (STM)
Root apical meristem
1 - Quiescent center
2 - Calyptrogen (live rootcap cells)
3 – Rootcap
4 - Rootcap cells
5 - Procambium
• The root apical meristem produces cells in two dimensions.
• It harbors two pools of stem cells around an organizing center called the quiescent center(QC) cells and together produce most of the cells in an adult root.
• QC : low mitotic activity.
Act as a reservoir of stem cells
• Root cap: protects and guide its growth
RAM
Root Cells
• Root structure
Root cap
• composed of inner columella cells and lateral root cap cells
• New root cap produced when existing cap is removed
• Zone of maturation
– cells differentiate into specific cell types
• root surface cells mature into epidermal hairs, each with root hair
• cortex produced by parenchyma cells– inner boundary differentiates into endodermis
» surrounded by Casparian strips composed of suberin
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The HOBBIT gene is required for root meristem, but not shoot meristem formation
Hobbit is a protein that inhibits another protein that stops the gene expression of the genes that Auxin causes to be made!!!!
Some Genes Involved in Root-Shoot Formation
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Two Internal Proteins Responsible for the Development of a Structure Cause Similar
Phenotypes if their corresponding genes are mutated
Has a basal peg not a rootAbnormal celldivision create stubrather than a root
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Auxin and Monopteros Promote Root Development
One way that auxin induces
gene expression is
by activating the
MONOPTEROS
(MP) protein
-Auxin releases the
repressor from MP
-MP then activates the
transcription of a
root development gene
• ”Auxin maximum” is required for RAM development.
• Root apical meristem protected by root cap.
Strigolactones (SLs) : Regulates shoot & root development.
• RAM size is controlled by DA1-Related Protein2 in Arabidopsis.
• ERECTA genes regulate auxin transport in SAM.
• SCARECROW function reveals a radial patterning in root & shoot.
• MADS box genes : Helps in development of Roots, Leaf, Flower, Ovule & fruit.
Conclusion
• SAM
SHOOT-MERISTEMLESS (STM),
WUSCHEL (WUS),
CLAVATA1 (CLV1)
CLAVATA3 (CLV3).
ERECTA genes
• RAM
DA1-Related Protein2
MONOPTEROS (MP)protein
HOBBIT gene
MADS box genes
SCR Mutants
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References
Plant roots – Amaram Eshel.
Plant physiology – A.S.Gontia.
www.wikipedia.com
www.DocStock.com
www.ncbi.nlm.nih.gov
www.researchgate.net
www.sciencedirect.com
Reviews & Research articles.
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