Trichome Development

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Trichome Development

• Trichome cell morphogenesis in Arabidopsis
• a continuum of cellular decisions
• Mathur, Jaldeep 2006

2
Trichomes/Epidermal hairs

• found on many plants in different shapes
• unicellular or multicellular
• branched or unbranched
• dendritic (tree-like), tufted, or stellate
  (star-shaped)

Grape
Elephants ear leaf (papillose)
Pupulus
Alfalfa
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Functions of trichomes

• 1. decrease heat and water loss by producing a
  thicker boundary layer on the plant
• 2. protection physical barriers to insects, UV
  irradiation
• 3. produce glands/secrete mucus or chemicals

Tillandsia
Stem of foxglove glandular trichome
(multicellular and uniseriate)
Protective Trichomes On Plants Capable Of
Causing Inflammation Trauma
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A. thaliana Trichomes

• 300-500µm tall
• Unicellular, branched (rosette leave)
• stellate (star-shaped)
• papillate cell wall
• As Protection
• three branches
• single nucleus located at the branching point.
• 4 endoreduplication cycles
• Most aerial parts, but not hypocotyl cotyledon
• Rosette leave 3-4 branches
• Cauline reduced branching
• Stem unbranched
• Density on abaxial side of leaves increased
  significantly
• from vegetative to reproductive growth
• First trichome appear
• when leaf grows to 100µm in length
• subset of trichome on leave,

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Trichome Morphogenesis

• Stage 1 Cell Enlargement
• (Patterning Endoreduplocation)
• Stage 2 Tubular Outgrowth
• Stage 3 Branch Initiation
• Stage 4 Extension
• Stage 5 Cell Maturation

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• An example of secondary trichomes (white arrows)
  initiating around an existing central trichome
  (black arrow)
• (1) isodiametric expansion in the plane of the
  epidermis
• (2) stalk emergence and polar expansion
• (3)branch initiation
• (4) expansion of the stalk, secondary branching
  and branches with a blunt tip morphology
• (5) trichome expansion with pointed branch tips
• (6) mature trichome with a papillate cell wall

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Stage 1 Cell enlargement

• Cell size a Nuclear DNA content
• 1st round of endoreduplication
• Enlargement and bulging (10-15µm) due to increase
  DNA content, cell turgor.
• (unclear on pH alterations, Ca2 gradient)
• Form Intracellular polarization
• GL2 mutant ? first enlarge but not proceed
  further, when lead expand, fall flat and visible
  as large slightly buldged cell
• Downstream target of GL2
• AtPLD?1 mediates plasma membrane modification
  (memebrane microtubule interaction)

Rerie et al. 1994
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Stage 2 Tubular outgrowth

• perpendicular , tubular form
• Vacuole become more prominent
• 2nd round of endoreduplication
• Might have actin-mediated tip growth with sharp
  tip
• SCD1 mutant, trichome stop growing at tubular
  stage and collapse when leaf expand
• Encode novel regulatory protein affecting vesicle
  transport

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Strong allele of STICHEL mutant show
needle-like, unbranched, tapering trichome
only Weak allele of STICHEL mutant show branch
initial Expressed in all organs, involved in
branch number too Single and double mutant
phenotypes of combinations with different sti
alleles. A, wild type B, sti-EMU C, sti-40 D,
double mutant sti-40 nok-122 E, double mutant
try-EM1 sti-40 F, double mutant sti-40 gl3 G,
double mutant sti-XT1 nok-122 H, triple mutant
try-EM1 sti-40 nok-122 I, triple mutant sti-40
nok-122 gl3 J, 35SSTI rosette leaf w/ 4
branches K, 35SSTI leaf trichome w/ 7
branches L, 35SSTI stem trichomes w/ branches
Ilgenfritz et al. 2003
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Stage 3 Branch Initiation

• From single axis of growth to multidirectional
  growth
• Microtubule cytoskeleton reorganization
• Selective stabilization of microtubules at plasma
  membrane
• Local stimulation of microtubule-serving proteins
• Microtubules-organizing/organelleinteracting
  properties of motor proteins like ZWICHEL, KIC
  Kinesin-13A regulators
• Stringent law of angular interaction
• Involved many genes and unclear

WT
stichell
zwichel
Schnittger et al. 2002)
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• wild-type
• zwi-3
• (C, E, G, I) WT
• (D, F, H, J) zwi-3
• at different stages of development
• Open arrow
• distal tip of the leaf blade
• Closed arrow
• 2nd focus of cell expansion, which produces 1st
  branch

Oppenheimer et al. 1997
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Stage 4 Branch Extension

• Distorted group
• CROOKED
• DISTORTED1
• DISTORTED2
• WURM, etc
• F-actin regulation

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Stage 5 Cell Maturation

• Formation of papillate secondary CW thickening
• Nearly unknown
• Only 5 mutants identified
• Glassy trichome phenotype
• Chablis, chardonnay, retsina, underdevelop
  trichome, trichome birefringence
• Encode CW component

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Microtubule (more spherical cell) Actin (smaller cell)
stabilizing Taxol phalloidin, jasplakinolide
depolymerizatioin Oryzalin, propyzamide cytochalasins, latrunculins
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Schellmann et al. 2005
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trichome
Root hair
Schellmann et al. 2005 Pesch et al. 2004
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TTG1, GL3, EGL3 and GL1/WER are thought to form
an active complex that bind to promoter regions
of downstream target genes to activate
transcription. TRY, CPC and ETC1 are postulated
to inhibit the activators by competing with GL1
or WER for their binding to GL3 or EGL3. The
complex containing TRY/CPC/ETC1 would be inactive
because it either does not bind to the promoter
anymore or is unable to activate transcription.
Pesch et al. 2004
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Szymanski et al. 2000