Transcript Bio 226: Cell and Molecular Biology

Pathogens
• Agrobacterium tumefaciens: Greg
• Agrobacterium rhizogenes
• Pseudomonas syringeae
• Pseudomonas aeruginosa: Mike
• Viroids: Bryant
• DNA viruses
• RNA viruses: Rob
• Fungi : Connor
• oomycetes
• Nematodes: Chris
Symbionts
• N-fixers
• Endomycorrhizae
• Ectomycorrhizae
Plant Growth
Size & shape depends on cell # & cell size
Decide which way to divide & which way to elongate
• Periclinal = perpendicular to surface: get longer
• Anticlinal = parallel to surface: add more layers
Now must decide which way to elongate: which walls to
stretch
Plant Cell Walls and Growth
Carbohydrate barrier
surrounding cell
• Protects & gives cell shape
• 1˚ wall made first
• mainly cellulose
• Can stretch!
• 2˚ wall made after growth
stops
• Lignins make it tough
Plant Cell Walls and Growth
Cellulose: ordered chains made of glucose linked b 1-4
• Cross-link with neighbors to form strong, stable fibers
• Made by enzyme embedded in the plasma membrane
• Guided by cytoskeleton
• Cells with poisoned µtubules are misshapen
• Other wall chemicals are made in Golgi & secreted
• Only cellulose pattern
is tightly controlled
Plant Cell Walls and Growth
Cellulose pattern is tightly controlled
• 6 CES enzymes form a “rosette”: each makes 6 chains
• Rosettes are guided by microtubules
• Deposition pattern determines direction of elongation
Plant Cell Walls and Growth
New fibers are perpendicular to growth direction, yet
fibers form a mesh
Multinet hypothesis: fibers reorient as cell elongates
Old fibers are anchored so gradually shift as cell grows
Plant Cell Walls and Growth
New fibers are perpendicular to growth direction, yet
fibers form a mesh
Multinet hypothesis: fibers reorient as cell elongates
Old fibers are anchored so gradually shift as cell grows
Result = mesh
Plant Cell Walls and Growth
1˚ walls = 25% cellulose, 25% hemicellulose, 35% pectin,
5% protein (but highly variable)
Hemicelluloses AKA cross-linking glycans: bind cellulose
Plant Cell Walls and Growth
Hemicelluloses AKA cross-linking glycans: bind cellulose
Coat cellulose & bind
neighbor
Plant Cell Walls and Growth
Hemicelluloses AKA cross-linking glycans
Coat cellulose & bind neighbor
Diverse group of glucans: also linked b 1-4, but may have
other sugars and components attached to C6
Hemicelluloses
Diverse group of glucans: also linked b 1-4, but may have
other sugars and components attached to C6
makes digestion more difficult
Hemicelluloses
Diverse group of glucans: also linked b 1-4, but may have
other sugars and components attached to C6
makes digestion more difficult
Assembled in Golgi
Plant Cell Walls and Growth
Hemicelluloses AKA cross-linking glycans
A diverse group of glucans also linked b 1-4, but may have
other sugars and components attached to C6
makes digestion more difficult
Assembled in Golgi
Secreted cf woven
Plant Cell Walls and Growth
1˚ walls = 25% cellulose, 25% hemicellulose, 35% pectin,
5% protein (but highly variable)
Pectins: fill space between cellulose-hemicellulose fibers
Pectins
Pectins: fill space between cellulose-hemicellulose fibers
Form gel that determines cell wall porosity(& makes jam)
Pectins
Pectins: fill space between cellulose-hemicellulose fibers
Form gel that determines cell wall porosity (& makes jam)
Acidic, so also modulate pH & bind polars
Pectins
Pectins: fill space between cellulose-hemicellulose fibers
Form gel that determines cell wall porosity (& makes jam)
Acidic, so also modulate pH & bind polars
Backbone is 1-4 linked galacturonic acid
Pectins
Backbone is 1-4 linked galacturonic acid
Have complex sugar side-chains, vary by spp.
Pectins
Backbone is 1-4 linked galacturonic acid
Have complex sugar side-chains, vary by spp.
Plant Cell Walls and Growth
Also 4 main multigenic families of structural proteins
Plant Cell Walls and Growth
Also 4 main multigenic families of structural proteins
Amounts vary between cell types & conditions
Plant Cell Walls and Growth
Also 4 main multigenic families of structural proteins
Amounts vary between cell types & conditions
1. HRGP: hydroxyproline-rich glycoproteins (eg extensin)
• Proline changed to hydroxyproline in Golgi
Plant Cell Wall Proteins
1. HRGP: hydroxyproline-rich glycoproteins (eg extensin)
• Proline changed to hydroxyproline in Golgi
• Highly glycosylated: helps bind CH2O
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Plant Cell Wall Proteins
HRGP: hydroxyproline-rich glycoproteins (eg extensin)
Proline changed to hydroxyproline in Golgi
Highly glycosylated: helps bind CH2O
Common in cambium, phloem
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Plant Cell Wall Proteins
HRGP: hydroxyproline-rich glycoproteins (eg extensin)
Proline changed to hydroxyproline in Golgi
Highly glycosylated: helps bind CH2O
Common in cambium, phloem
Help lock the wall after growth ceases
Plant Cell Wall Proteins
1. HRGP: hydroxyproline-rich glycoproteins (eg extensin)
• Proline changed to hydroxyproline in Golgi
• Highly glycosylated: helps bind CH2O
• Common in cambium, phloem
• Help lock the wall after growth ceases
• Induced by wounding
2. PRP: proline-rich proteins
Plant Cell Wall Proteins
1. HRGP: hydroxyproline-rich glycoproteins (eg extensin)
2. PRP: proline-rich proteins
• Low glycosylation = little interaction with CH2O
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Plant Cell Wall Proteins
HRGP: hydroxyproline-rich glycoproteins (eg extensin)
PRP: proline-rich proteins
Low glycosylation = little interaction with CH2O
Common in xylem, fibers, cortex
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Plant Cell Wall Proteins
HRGP: hydroxyproline-rich glycoproteins (eg extensin)
PRP: proline-rich proteins
Low glycosylation = little interaction with CH2O
Common in xylem, fibers, cortex
May help lock HRGPs together
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Plant Cell Wall Proteins
HRGP: hydroxyproline-rich glycoproteins (eg extensin)
PRP: proline-rich proteins
Low glycosylation = little interaction with CH2O
Common in xylem, fibers, cortex
May help lock HRGPs together
GRP: Glycine-rich proteins
No glycosylation = little interaction with CH2O
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Plant Cell Wall Proteins
HRGP: hydroxyproline-rich glycoproteins (eg extensin)
PRP: proline-rich proteins
Low glycosylation = little interaction with CH2O
Common in xylem, fibers, cortex
May help lock HRGPs together
GRP: Glycine-rich proteins
No glycosylation = little interaction with CH2O
Common in xylem
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Plant Cell Wall Proteins
HRGP: hydroxyproline-rich glycoproteins (eg extensin)
PRP: proline-rich proteins
Low glycosylation = little interaction with CH2O
Common in xylem, fibers, cortex
May help lock HRGPs together
GRP: Glycine-rich proteins
No glycosylation = little interaction with CH2O
Common in xylem
May help lock HRGPs & PRPs together
Plant Cell Wall Proteins
1. HRGP: hydroxyproline-rich glycoproteins (eg extensin)
2. PRP: proline-rich proteins
3. GRP: Glycine-rich proteins
• No glycosylation = little interaction with CH2O
• Common in xylem
• May help lock HRGPs & PRPs together
4. Arabinogalactan proteins
Plant Cell Wall Proteins
1. HRGP: hydroxyproline-rich glycoproteins (eg extensin)
2. PRP: proline-rich proteins
3. GRP: Glycine-rich proteins
4. Arabinogalactan proteins
• Highly glycosylated: helps bind CH2O
Plant Cell Wall Proteins
1. HRGP: hydroxyproline-rich glycoproteins (eg extensin)
2. PRP: proline-rich proteins
3. GRP: Glycine-rich proteins
4. Arabinogalactan proteins
• Highly glycosylated: helps bind CH2O
• Anchored to PM by GPI
Plant Cell Wall Proteins
1. HRGP: hydroxyproline-rich glycoproteins (eg extensin)
2. PRP: proline-rich proteins
3. GRP: Glycine-rich proteins
4. Arabinogalactan proteins
• Highly glycosylated: helps bind CH2O
• Anchored to PM by GPI
• Help cell adhesion and cell signaling
Plant Cell Wall Proteins
1. HRGP: hydroxyproline-rich glycoproteins (eg extensin)
2. PRP: proline-rich proteins
3. GRP: Glycine-rich proteins
4. Arabinogalactan proteins
• Highly glycosylated: helps bind CH2O
• Anchored to PM by GPI
• Help cell adhesion and cell signaling
5. Also many enzymes involved in cell wall synthesis and
loosening
Plant Cell Walls and Growth
Also many enzymes involved in cell wall synthesis and
loosening
As growth stops, start making lignins & linking HGRP
Plant Cell Walls and Growth
As growth stops, start depositing lignins & linking HGRP
Lignins = polyphenolic macromolecules: 2nd most
abundant on earth (after cellulose)
Plant Cell Walls and Growth
Lignins = polyphenolic macromolecules: 2nd most
abundant on earth (after cellulose)
Bond hemicellulose: solidify & protect cell wall (nature’s
cement): very difficult to digest
Plant Cell Walls and Growth
Lignins = polyphenolic macromolecules: 2nd most
abundant on earth (after cellulose)
Bond hemicellulose: solidify & protect cell wall (nature’s
cement): very difficult to digest
Monomers are made in cytoplasm & secreted
Plant Cell Walls and Growth
Monomers are made in cytoplasm & secreted
Peroxidase & laccase in cell wall create radicals that
polymerise non-enzymatically
Plant Cell Walls and Growth
Monomers are made in cytoplasm & secreted
Peroxidase & laccase in cell wall create radicals that
polymerise non-enzymatically
Plant Cell Walls and Growth
Peroxidase & laccase in cell wall create radicals that
polymerise non-enzymatically
Very difficult to digest, yet major plant component!
Plant Cell Walls and Growth
As growth stops, start depositing lignins & linking HGRP
Solidify & protect cell wall: very difficult to digest
Elongation precedes lignification
Plant Cell Walls and Growth
As growth stops, start depositing lignins & linking HGRP
Solidify & protect cell wall: very difficult to digest
Elongation precedes lignification
Requires loosening the bonds joining the cell wall
Plant Cell Walls and Growth
Elongation precedes lignification
Requires loosening the bonds joining the cell wall
Can’t loosen too much or cell will burst
Plant Cell Walls and Growth
Elongation precedes lignification
Requires loosening the bonds joining the cell wall
Can’t loosen too much or cell will burst
Must coordinate with cell wall synthesis so wall stays same
Plant Cell Walls and Growth
Elongation: loosening the bonds joining the cell wall
Can’t loosen too much or cell will burst
Must coordinate with cell wall synthesis so wall stays same
Must weaken crosslinks joining cellulose fibers
Plant Cell Walls and Growth
Must weaken crosslinks joining cellulose fibers
Turgor pressure then makes cells expand
Plant Cell Walls and Growth
Must weaken crosslinks joining cellulose fibers
Turgor pressure then makes cells expand
• Lower pH: many studies show that lower pH is
sufficient for cell elongation
Plant Cell Walls and Growth
Must weaken crosslinks joining cellulose fibers
• Lower pH: many studies show that lower pH is
sufficient for cell elongation
Acid growth hypothesis: Growth regulators cause
elongation by activating H+ pump
Plant Cell Walls and Growth
Acid growth hypothesis: Growth regulators cause
elongation by activating H+ pump
• Inhibitors of H+ pump stop elongation
• But: Cosgrove isolated proteins that loosen cell wall
• Test protein extracts
to see if wall loosens
Plant Cell Walls and Growth
Acid growth hypothesis: Growth regulators cause
elongation by activating H+ pump
• But: Cosgrove isolated proteins that loosen cell wall
• Test protein extracts to see if wall loosens
• Identified expansin proteins that enhance acid growth
Plant Cell Walls and Growth
Acid growth hypothesis: Growth regulators cause
elongation by activating H+ pump
• But: Cosgrove isolated proteins that loosen cell wall
• Test protein extracts to see if wall loosens
• Identified expansin proteins that enhance acid growth
• Still don’t know how they work!
Plant Cell Walls and Growth
• Identified expansin proteins that enhance acid growth
• Still don’t know how they work!
• Best bet, loosen Hemicellulose/cellulose bonds
Plant Cell Walls and Growth
Also have endoglucanases and transglucanases that cut &
reorganize hemicellulose & pectin
Plant Cell Walls and Growth
Also have endoglucanases and transglucanases that cut &
reorganize hemicellulose & pectin
XET (xyloglucan endotransglucosylase) is best-known
Plant Cell Walls and Growth
Also have endoglucanases and transglucanases that cut &
reorganize hemicellulose & pectin
XET (xyloglucan endotransglucosylase) is best-known
Cuts & rejoins hemicellulose
in new ways
Plant Cell Walls and Growth
XET is best-known
Cuts & rejoins hemicellulose
in new ways
Expansins & XET catalyse cell
wall creepage
Plant Cell Walls and Growth
XET is best-known
Cuts & rejoins hemicellulose in new ways
Expansins & XET catalyse cell wall creepage
Updated acid growth hypothesis: main function of
lowering pH is activating expansins and glucanases
Plant Cell Walls and Growth
Updated acid growth hypothesis: main function of
lowering pH is activating expansins and glucanases
Coordinated with synthesis of new cell wall to keep
thickness constant
Plant Cell Walls and Signaling
Pathogens must digest cell wall to enter plant
Plant Cell Walls and Signaling
Pathogens must digest cell wall to enter plant
Release cell wall fragments
Plant Cell Walls and Signaling
Pathogens must digest cell wall to enter plant
Release cell wall fragments
Many oligosaccharides signal”HELP!”
Plant Cell Walls and Signaling
Pathogens must digest cell wall to enter plant
Release cell wall fragments
Many oligosaccharides signal”HELP!”
Elicit plant defense responses