The document discusses meristematic tissues and apical meristems in plants. It summarizes that the shoot apical meristem (SAM) and root apical meristem (RAM) contain stem cells and are responsible for postembryonic growth. The SAM contains four distinct cell groups and is maintained by genes like SHOOT MERISTEMLESS, WUSCHEL, and CLAVATA1/3. The RAM contains a quiescent center and produces root cells. Key genes that regulate SAM and RAM development include MONOPTEROS and HOBBIT.

1. TILAK. I S
PG14AGR6074

2. 2
Introduction
Meristem
SAM
contents
RAM
Conclusions
Molecular Analysis
Of SAM & RAM

3. INTRODUCTION
• Plant Tissues fall into two
large categories:
Meristematic.
Permanent (Non-
Meristematic)
Term”meristem” was first used in
1858 by Carl Wilh. V. Nagell

4. meristem
 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
Tunica determine the physical
characteristics of the leaf edge and
margin.

5. Positional information (auxin
accumulation) precedes leaf initiation
Auxin accumulation
precedes leaf initiation
Indole-3-acetic acid (IAA) a
naturally occurring auxin

6. 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

7. 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.

8. Apical Meristems
• In plants belonging to the MONOCOT , apical
meristems are located ONLY in the root tips.
• REVOLUTA gene is necessary for Apical meristem
development

9. STM and CUC1 Expression (Apical Meristem)
• CUC1 redundantly required for embryonic apical meristem
formation, cotyledon separation and expression of STM..
Cup shaped cotyledon

10. 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.

11. 11

12. (Jean et al.,2007) 12

13. Shoot apical meristems
• 14 days later, leaves have developed (right).

14. 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
14

15. 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

16. Shoot apical meristem organization
Stem Cells
Central Zone
L1 = tunica
L2 = tunica
Peripheral Zone
Pith or Rib
Meristem
Organizing Center
L3 = corpus
16

17. Development involves positional
information
Auxin gradients are regulated by auxin
transporters)
Movement of a signal away
from a source
… selective destruction
of a signal by miRNA
cleavage of mRNAs)
REVOLUTA gene is necessary for Apical meristem development

18. Development involves boundaries
Boundaries form between the shoot
apical meristem and leaf primordia,
and between the upper and lower
surfaces of the leaf
Shoot apical
meristem
Patterning of cells in
the epidermis also
involves production of
inhibitory signals

19. Genes necessary for (SAM)
 SHOOT- MERISTEMLESS (STM) Late globular embryo.
 WUSCHEL (WUS) Early Globular stage @ cells
below the stem cells
 CLAVATA1 (CLV1)
 CLAVATA3 (CLV3)
Early Heart – shaped embryo Size ,
• SAM becomes distinquishable at torpedo stage.
Cell division
Signalling

24. 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 kinase
receptor.
24
(Thomas et al.,2008)

25. Shoot Development : Genetics
CLAVATA gene mechanism
Protein-binding
motif
CLAVATA GENE Characteristics
CLV1 – Extracellular polypeptide: 96 amino acids
Restricted to L1, L2 of SAM Central Zone
CLV2 – Membrane-bound protein receptor with a protein-binding motif
CLV3 – Membrane-bound protein receptor with a protein-binding motif and
Restricted to L1, L2 of SAM Central Zone
Kinase activity… signaling… Kinase cascade
Inhibitory to WUS expression
Signal transduction pathway

26. WUSCHEL(WUS) molecular mechanism
WUS function:
1. WUS Protein product is a homeodomain
transcription factor
2. Gene regulation
3. Positional influence of once cell type by
another
• wus mutants result in
1. Early termination of SAM
 wus defective in maintaining SAM
2. Aberrant SAM organization
 wus defective in maintaining SAM
integrity
L1
L2
L3
Localization of WUS gene
product in organizing
center (OC) of shoot
26

27. Shoot Development : Genetics
WUSCHEL gene phenotype
Wild Type
wus mutant
Wild type SAM
wus SAM
mutants but it fails to develop

28. Gene Interaction: WUSCHEL and CLAVATA
Initiation of an Organizing Center in the shoot apical meristem
CLV3 expression
( Cell division )
WUS expression ( Gene Regulation )
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)

29. mRNA Expression Domains and gene interaction
for CLV1 CLV3 and WUS
Wild type
clv mutant
wus
mutant
Overexpressed
WUS mutant
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)

30. A feedback look between WUS and CLV exists because:
1. Expansion of the WUS expression domain in a clv
mutant suggests a feedback loop between the two
genes.
2. wus mutants have downregulated (smaller) CLV3
expression domain.
3. WUS overexpressed mutants have a broader CLV3
expression domain.

31. Shoot Development II: Genetics
CLAVATA gene phenotype
Normal SAM
clavata SAM
CLV localization in Central
Zone of SAM
1. CLV localization in Central Zone of SAM
2. Mutant phenotype: Huge apical meristems
 CLV wild type restricts stem cell accumulation

32. STM molecular mechanism
– Stem cells of Central Zone and
peripheral Zone.
– Encodes homeodomain protein
KNOTTED Class
– Transcription factor
– Prevents premature
differentiation of cells from
Peripheral Zone.
Wild type Stm mutant
32

33. -STM encodes a
transcription factor
with homeobox region Cotyledons not mature leaves
33
Some Genes Involved in Root-Shoot
Formation
Both shoot and root meristems are apical
meristems, but are independently controlled
-Shootmeristemless
(STM) is necessary for
stm mutant
shoot formation, but
not root development
STM wild type
are shown

34. Gene Expression in the Apical Embryo Domain
WUSCHEL (WUS), CLAVATA (CLV) AND SHOOT MERISTEMLESS (STM)
Laux, T., et al. Plant Cell 2004;16:S190-S202

35. Root apical meristem
1 - Quiescent center
2 - Calyptrogen (live rootcap cells)
3 – Rootcap
4 - Rootcap cells
5 - Procambium

38. • 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

39. RAM

40. 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

41. • 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

42. Some Genes Involved in Root-Shoot
Formation
The HOBBIT gene is required for root meristem, but not
shoot meristem formation
42
Hobbit is a protein that inhibits another protein that stops
the gene expression of the genes that Auxin causes to be
made!!!!

43. 43
Two Internal Proteins Responsible for the
Development of a Structure Cause Similar
Phenotypes if their corresponding genes are
mutated
Abnormal cell Has a basal peg not a root
division create stub
rather than a root

44. 44
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

45. • ”Auxin maximum” is required for RAM
development.
• Root apical meristem protected by root cap.
 Strigolactones (SLs) : Regulates shoot & root
development.

46. • 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.

47. 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
47

48. 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.

49. THANK YOU