Pathogens• Agrobacterium tumefaciens • Agrobacterium rhizogenes• Pseudomonas syringeae• Pseudomonas aeruginosa• Viroids• DNA viruses• RNA viruses• Fungi• oomycetes• nematodes

Symbionts• N-fixers• Endomycorrhizae• Ectomycorrhizae

Plant GrowthDecide which way to divide & which way to elongate• Periclinal = perpendicular to surface: get longer• Anticlinal = parallel to surface: add more layersNow must decide which way to elongate: which walls to

stretch

Plant Cell Walls and GrowthCarbohydrate barriersurrounding 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• 1˚ wall made first•mainly cellulose•Can stretch! Control elongation by controlling orientation of cell wall fibers as wall is made•1˚ walls = 25% cellulose, 25% hemicellulose, 35% pectin, 5% protein (but highly variable)

Plant Cell Walls and Growth1˚ walls = 25% cellulose, 25% hemicellulose, 35% pectin,

5% protein (but highly variable)Cellulose: ordered chains made of glucose linked1-4• Cross-link with neighbors to form strong, stable fibers

Plant Cell Walls and GrowthCellulose: ordered chains made of glucose linked 1-4• Cross-link with neighbors to form strong, stable fibers• Made by enzyme embedded in the plasma membrane

Plant Cell Walls and GrowthCellulose: ordered chains made of glucose linked 1-4• Cross-link with neighbors to form strong, stable fibers• Made by enzyme embedded in the plasma membrane• Guided by cytoskeleton

Plant Cell Walls and GrowthCellulose: ordered chains made of glucose linked 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

Plant Cell Walls and GrowthCellulose: ordered chains made of glucose linked 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

Plant Cell Walls and GrowthCellulose: ordered chains made of glucose linked 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 GrowthCellulose pattern is tightly controlled• 6 CES enzymes form a “rosette”: each makes 6 chains

-> 36/fiber

Plant Cell Walls and GrowthCellulose pattern is tightly controlled• 6 CES enzymes form a “rosette”: each makes 6 chains

-> 36/fiber• Rosettes are guided by microtubules

Plant Cell Walls and GrowthCellulose 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 GrowthCellulose pattern is tightly controlled• Deposition pattern determines direction of elongation• New fibers are perpendicular to growth direction, yet

fibers form a mesh

Plant Cell Walls and GrowthNew fibers are perpendicular to growth direction, yet

fibers form a meshMultinet hypothesis: fibers reorient as cell elongatesOld fibers are anchored so gradually shift as cell grows

Plant Cell Walls and GrowthNew fibers are perpendicular to growth direction, yet

fibers form a meshMultinet hypothesis: fibers reorient as cell elongatesOld fibers are anchored so gradually shift as cell growsResult = mesh

Plant Cell Walls and Growth1˚ walls = 25% cellulose, 25% hemicellulose, 35% pectin,

5% protein (but highly variable)Hemicelluloses AKA cross-linking glycans: bind cellulose

Plant Cell Walls and GrowthHemicelluloses AKA cross-linking glycans: bind celluloseCoat cellulose & bindneighbor

Plant Cell Walls and GrowthHemicelluloses AKA cross-linking glycansCoat cellulose & bind neighborDiverse group of glucans: also linked 1-4, but may have

other sugars and components attached to C6

HemicellulosesDiverse group of glucans: also linked 1-4, but may have

other sugars and components attached to C6 makes digestion more difficult

HemicellulosesDiverse group of glucans: also linked 1-4, but may have

other sugars and components attached to C6 makes digestion more difficultAssembled in Golgi

Plant Cell Walls and GrowthHemicelluloses AKA cross-linking glycansA diverse group of glucans also linked 1-4, but may

have other sugars and components attached to C6makes digestion more difficultAssembled in GolgiSecreted cf woven

Plant Cell Walls and Growth1˚ walls = 25% cellulose, 25% hemicellulose, 35% pectin,

5% protein (but highly variable)Pectins: fill space between cellulose-hemicellulose fibers

PectinsPectins: fill space between cellulose-hemicellulose fibersForm gel that determines cell wall porosity(& makes jam)

PectinsPectins: fill space between cellulose-hemicellulose fibersForm gel that determines cell wall porosity (& makes jam)Acidic, so also modulate pH & bind polars

PectinsPectins: fill space between cellulose-hemicellulose fibersForm gel that determines cell wall porosity (& makes jam)Acidic, so also modulate pH & bind polarsBackbone is 1-4 linked galacturonic acid

PectinsBackbone is 1-4 linked galacturonic acidHave complex sugar side-chains, vary by spp.

PectinsBackbone is 1-4 linked galacturonic acidHave complex sugar side-chains, vary by spp.

Plant Cell Walls and GrowthAlso 4 main multigenic families of structural proteins

Plant Cell Walls and GrowthAlso 4 main multigenic families of structural proteinsAmounts vary between cell types & conditions

Plant Cell Walls and GrowthAlso 4 main multigenic families of structural proteinsAmounts vary between cell types & conditions1. HRGP: hydroxyproline-rich glycoproteins (eg extensin)• Proline changed to hydroxyproline in Golgi

Plant Cell Wall Proteins1. HRGP: hydroxyproline-rich glycoproteins (eg extensin)• Proline changed to hydroxyproline in Golgi• Highly glycosylated: helps bind CH2O

Plant Cell Wall Proteins1. HRGP: hydroxyproline-rich glycoproteins (eg extensin)• Proline changed to hydroxyproline in Golgi• Highly glycosylated: helps bind CH2O• Common in cambium, phloem

Plant Cell Wall Proteins1. 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 Proteins1. 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 wounding2. PRP: proline-rich proteins

Plant Cell Wall Proteins1. HRGP: hydroxyproline-rich glycoproteins (eg extensin)2. PRP: proline-rich proteins• Low glycosylation = little interaction with CH2O

Plant Cell Wall Proteins1. HRGP: hydroxyproline-rich glycoproteins (eg extensin)2. PRP: proline-rich proteins• Low glycosylation = little interaction with CH2O• Common in xylem, fibers, cortex

Plant Cell Wall Proteins1. HRGP: hydroxyproline-rich glycoproteins (eg extensin)2. PRP: proline-rich proteins• Low glycosylation = little interaction with CH2O• Common in xylem, fibers, cortex• May help lock HRGPs together

Plant Cell Wall Proteins1. HRGP: hydroxyproline-rich glycoproteins (eg extensin)2. PRP: proline-rich proteins• Low glycosylation = little interaction with CH2O• Common in xylem, fibers, cortex• May help lock HRGPs together3. GRP: Glycine-rich proteins• No glycosylation = little interaction with CH2O

Plant Cell Wall Proteins1. HRGP: hydroxyproline-rich glycoproteins (eg extensin)2. PRP: proline-rich proteins• Low glycosylation = little interaction with CH2O• Common in xylem, fibers, cortex• May help lock HRGPs together3. GRP: Glycine-rich proteins• No glycosylation = little interaction with CH2O• Common in xylem

Plant Cell Wall Proteins1. HRGP: hydroxyproline-rich glycoproteins (eg extensin)2. PRP: proline-rich proteins• Low glycosylation = little interaction with CH2O• Common in xylem, fibers, cortex• May help lock HRGPs together3. GRP: Glycine-rich proteins• No glycosylation = little interaction with CH2O• Common in xylem• May help lock HRGPs & PRPs together

Plant Cell Wall Proteins1. HRGP: hydroxyproline-rich glycoproteins (eg extensin)2. PRP: proline-rich proteins3. GRP: Glycine-rich proteins• No glycosylation = little interaction with CH2O• Common in xylem• May help lock HRGPs & PRPs together4. Arabinogalactan proteins

Plant Cell Wall Proteins1. HRGP: hydroxyproline-rich glycoproteins (eg extensin)2. PRP: proline-rich proteins3. GRP: Glycine-rich proteins4. Arabinogalactan proteins• Highly glycosylated: helps bind CH2O

Plant Cell Wall Proteins1. HRGP: hydroxyproline-rich glycoproteins (eg extensin)2. PRP: proline-rich proteins3. GRP: Glycine-rich proteins4. Arabinogalactan proteins• Highly glycosylated: helps bind CH2O• Anchored to PM by GPI

Plant Cell Wall Proteins1. HRGP: hydroxyproline-rich glycoproteins (eg extensin)2. PRP: proline-rich proteins3. GRP: Glycine-rich proteins4. Arabinogalactan proteins• Highly glycosylated: helps bind CH2O• Anchored to PM by GPI• Help cell adhesion and cell signaling

Plant Cell Wall Proteins1. HRGP: hydroxyproline-rich glycoproteins (eg extensin)2. PRP: proline-rich proteins3. GRP: Glycine-rich proteins4. Arabinogalactan proteins• Highly glycosylated: helps bind CH2O• Anchored to PM by GPI• Help cell adhesion and cell signaling5. Also many enzymes involved in cell wall synthesis and

loosening

Plant Cell Walls and GrowthAlso many enzymes involved in cell wall synthesis and

looseningAs growth stops, start making lignins & linking HGRP

Plant Cell Walls and GrowthAs growth stops, start depositing lignins & linking HGRPLignins = polyphenolic macromolecules: 2nd most

abundant on earth (after cellulose)

Plant Cell Walls and GrowthLignins = 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 GrowthLignins = polyphenolic macromolecules: 2nd most

abundant on earth (after cellulose)Bond hemicellulose: solidify & protect cell wall (nature’s

cement): very difficult to digestMonomers are made in cytoplasm & secreted

Plant Cell Walls and GrowthMonomers are made in cytoplasm & secretedPeroxidase & laccase in cell wall create radicals that

polymerise non-enzymatically

Plant Cell Walls and GrowthMonomers are made in cytoplasm & secretedPeroxidase & laccase in cell wall create radicals that

polymerise non-enzymatically

Plant Cell Walls and GrowthPeroxidase & laccase in cell wall create radicals that

polymerise non-enzymaticallyVery difficult to digest, yet major plant component!

Plant Cell Walls and GrowthAs growth stops, start depositing lignins & linking HGRPSolidify & protect cell wall: very difficult to digestElongation precedes lignification

Plant Cell Walls and GrowthAs growth stops, start depositing lignins & linking HGRPSolidify & protect cell wall: very difficult to digestElongation precedes lignificationRequires loosening the bonds joining the cell wall

Plant Cell Walls and GrowthElongation precedes lignificationRequires loosening the bonds joining the cell wallCan’t loosen too much or cell will burst

Plant Cell Walls and GrowthElongation precedes lignificationRequires loosening the bonds joining the cell wallCan’t loosen too much or cell will burstMust coordinate with cell wall synthesis so wall stays same

Plant Cell Walls and GrowthElongation: loosening the bonds joining the cell wallCan’t loosen too much or cell will burstMust coordinate with cell wall synthesis so wall stays sameMust weaken crosslinks joining cellulose fibers

Plant Cell Walls and GrowthMust weaken crosslinks joining cellulose fibersTurgor pressure then makes cells expand

Plant Cell Walls and GrowthMust weaken crosslinks joining cellulose fibersTurgor pressure then makes cells expand• Lower pH: many studies show that lower pH is

sufficient for cell elongation

Plant Cell Walls and GrowthMust weaken crosslinks joining cellulose fibers• Lower pH: many studies show that lower pH is

sufficient for cell elongationAcid growth hypothesis: Growth regulators cause

elongation by activating H+ pump

Plant Cell Walls and GrowthAcid 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 GrowthAcid 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 GrowthAcid 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 GrowthAlso have endoglucanases and transglucanases that cut &

reorganize hemicellulose & pectin

Plant Cell Walls and GrowthAlso have endoglucanases and transglucanases that cut &

reorganize hemicellulose & pectin XET (xyloglucan endotransglucosylase) is best-known

Plant Cell Walls and GrowthAlso have endoglucanases and transglucanases that cut &

reorganize hemicellulose & pectin XET (xyloglucan endotransglucosylase) is best-knownCuts & rejoins hemicellulose in new ways

Plant Cell Walls and GrowthXET is best-knownCuts & rejoins hemicellulose in new waysExpansins & XET catalyse cell wall creepage

Plant Cell Walls and GrowthXET is best-knownCuts & rejoins hemicellulose in new waysExpansins & XET catalyse cell wall creepageUpdated acid growth hypothesis: main function of

lowering pH is activating expansins and glucanases

Plant Cell Walls and GrowthUpdated acid growth hypothesis: main function of

lowering pH is activating expansins and glucanasesCoordinated with synthesis of new cell wall to keep

thickness constant

Plant Cell Walls and SignalingPathogens must digest cell wall to enter plant

Plant Cell Walls and SignalingPathogens must digest cell wall to enter plantRelease cell wall fragments

Plant Cell Walls and SignalingPathogens must digest cell wall to enter plantRelease cell wall fragmentsMany oligosaccharides signal”HELP!”

Plant Cell Walls and SignalingPathogens must digest cell wall to enter plantRelease cell wall fragmentsMany oligosaccharides signal”HELP!”Elicit plant defense responses

Growth regulators1.Auxins2.Cytokinins3.Gibberellins4.Abscisic acid5.Ethylene6.BrassinosteroidsAll are small organics: made inone part, affectanother part

Growth regulatorsAll are small organics: made in one part, affect another partTreating a plant tissue with a hormone is like putting a dime in a vending machine. It depends on the machine, not the dime!

AuxinFirst studied by Darwins!Showed that a "transmissible influence" made at tips caused bending lower down

AuxinFirst studied by Darwins!Showed that a "transmissible influence" made at tips caused bending lower downNo tip, no curve!

AuxinFirst studied by Darwins!Showed that a "transmissible influence" made at tips caused bending lower downNo tip, no curve!1913:Boysen-Jensen showed that diffused through agar blocks but not through mica

Auxin1913:Boysen-Jensen showed that diffused through agar blocks but not through mica1919: Paal showed that if tip was replaced asymmetrically, plant grew asymmetrically even in dark

Auxin1913:Boysen-Jensen showed that diffused through agar blocks but not through mica1919: Paal showed that if tip was replaced asymmetrically, plant grew asymmetrically even in darkUneven amounts of "transmissible influence" makes bend

Auxin1919: Paal showed that if tip was replaced asymmetrically, plant grew asymmetrically even in darkUneven amounts of "transmissible influence" makes bend1926: Went showed that a chemical that diffused from tips into blocks caused growth

Auxin1919: Paal showed that if tip was replaced asymmetrically, plant grew asymmetrically even in darkUneven amounts of "transmissible influence" makes bend1926: Went showed that a chemical that diffused from tips into blocks caused growthIf placed asymmetrically get bending due to asymmetrical growth

Auxin1919: Paal showed that if tip was replaced asymmetrically, plant grew asymmetrically even in darkUneven amounts of "transmissible influence" makes bend1926: Went showed that a chemical that diffused from tips into blocks caused growthIf placed asymmetrically get bending due to asymmetrical growthAmount of bending depends on [auxin]

Auxin1919: Paal showed that if tip was replaced asymmetrically, plant grew asymmetrically even in darkUneven amounts of "transmissible influence" makes bend1926: Went showed that a chemical that diffused from tips into blocks caused growthIf placed asymmetrically get bending due to asymmetrical growthAmount of bending depends on [auxin]1934: Indole-3-Acetic acid (IAA) from the urine of pregnant women was shown to cause bending

Auxin1934: Indole-3-Acetic acid (IAA) from the urine of pregnant women was shown to cause bendingIAA is the main auxin in vivo.Others include Indole-3-butyric acid (IBA), 4-Chloroindole-3-acetic acid and phenylacetic acid (PA)

IBAIBA

PAPA4-CI-IAA

IAAIAA

AuxinIAA is the main auxin in vivo.Many synthetic auxins have been identified

IAAIAA

AuxinIAA is the main auxin in vivo.Many synthetic auxins have been identifiedNo obvious structural similarity, yet all work!

IAAIAA

AuxinIAA is the main auxin in vivo.Many synthetic auxins have been identifiedNo obvious structural similarity, yet all work!Widely used in agriculture

IAAIAA

AuxinIAA is the main auxin in vivo.Many synthetic auxins have been identifiedNo obvious structural similarity, yet all work!Widely used in agriculture • to promote growth (flowering, cuttings)

IAAIAA

AuxinIAA is the main auxin in vivo.Many synthetic auxins have been identifiedNo obvious structural similarity, yet all work!Widely used in agriculture • to promote growth (flowering, cuttings)• as weed killers!

Agent orange was 1:1 2,4-D and 2,4,5-T

IAAIAA