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 HRGP: hydroxyproline-rich glycoproteins (eg extensin) Proline changed to hydroxyproline in Golgi

Plant Cell Wall Proteins HRGP: hydroxyproline-rich glycoproteins (eg extensin) Proline changed to hydroxyproline in Golgi Highly glycosylated: helps bind CH2O

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

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 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 HRGP: hydroxyproline-rich glycoproteins (eg extensin) PRP: proline-rich proteins Low glycosylation = little interaction with CH2O

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

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

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

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

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 HRGP: hydroxyproline-rich glycoproteins (eg extensin) 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 HRGP: hydroxyproline-rich glycoproteins (eg extensin) PRP: proline-rich proteins 3. GRP: Glycine-rich proteins 4. Arabinogalactan proteins Highly glycosylated: helps bind CH2O

Plant Cell Wall Proteins HRGP: hydroxyproline-rich glycoproteins (eg extensin) 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 HRGP: hydroxyproline-rich glycoproteins (eg extensin) 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 HRGP: hydroxyproline-rich glycoproteins (eg extensin) 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