Desiccation Tolerance Mechanisms and Evolution

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Desiccation ToleranceMechanisms and Evolution
Mel Oliver and Brent Mishler
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Desiccation-tolerance.

• The ability to revive from the air-dried state
  (the air being of low relative humidity) thus
  experiencing protoplasmic dehydration without
  suffering permanent injury
• Bewley and Krochko. 1982

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Types of Desiccation-tolerance.

• Plants whose tolerance to water loss is low.
• Plant structures that are adapted to withstand
  desiccation and for which water loss is an
  expected event. - seeds.
• Plants that are capable of tolerating desiccation
  regardless of the rate at which water loss
  occurs.
• Plants that are capable of tolerating desiccation
  only if water loss is a slow process.

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Desiccation-tolerant Plants.

• Desiccation-tolerant
• ALGAE
• LICHENS
• BRYOPHYTES
• Modified Desiccation-tolerant
• FERNS
• ANGIOSPERMS

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Distribution of Desiccation Tolerance in the
Plant Kingdom
Angiosperms
conifers
cycads
ferns
gnetophytes
Equisetum
Gingko
Selaginella
Isoetes
Lycopodium
mosses
hornworts
liverworts
Seed Plants
Tracheophytes
Land Plants
Oliver, Tuba and Mishler 2000
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Tortula ruralis
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Selaginella
Selaginella bigelovii
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Polypodium virginianum
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Orthodox Seeds
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Distribution of Desiccation tolerance in the
Angiosperms
Cyperaceae
Labiatae
Poaceae
Scrophulariaceae
Gesneriaceae
Velloziaceae
Liliaceae
Hamameliales
Magnoliales
renunculids
Angiosperms
Oliver, Tuba and Mishler 2000
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Xerophyta villosa
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Myrothamnus flabellifolia
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Craterostigma wilmsii
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Xerophyta viscosa
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Sporobolus stapfianus
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Craterostigma plantagineum
Hydrated
Dry
Rehydrated
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Critical Parameters for Desiccation-tolerance.

• Limit damage to a repairable level
• Maintain physiological integrity in the dry
  state
• Mobilize repair mechanisms upon rehydration

Bewley 1979
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Essence of Desiccation-tolerance.

• Testable Hypothesis

Cellular Repair
Cellular Protection
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Bryophyte Model
RAPID WATER LOSS Constitutive Cellular Protection
Hormone ?
Induction of Recovery and Repair Mechanisms
Hydrated
Dry
Rehydrated
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Angiosperm Model
SLOW WATER LOSS Induction of Cellular Protection
ABA
Re-establishment Processes
Hydrated
Dry
Rehydrated
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Postulated Evolutionary History of Desiccation
Tolerance in Land Plants
Angiosperms
conifers
cycads
ferns
gnetophytes
Inducible protection (repair?) and
later poikilochlorophylly
Equisetum
Gingko
Selaginella
Isoetes
Lycopodium
S
mosses
Developmentally programmed protection - propagules
hornworts
liverworts
Inducible protection plus repair?
T
Developmentally programmed protection - spores?
Constitutive protection and repair
Loss of vegetative desiccation tolerance in the
ancestral lineage
Oliver, Tuba and Mishler 2000
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Bryophyte Model
RAPID WATER LOSS Constitutive Cellular Protection
Hormone ?
Induction of Recovery and Repair Mechanisms
Hydrated
Dry
Rehydrated
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Tr 288 Phylogenetic Gene Search
Tr 288 Gene
Expected PCR Products
(Sequence for Identity)
GPN-Box Consensus primers
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(No Transcript)
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Unrooted Tortula Phylogenetic Network Occurance
of Tr288 Orthologs
Probable tree root
Calyptopogon
288
Tortula papillosa
288
Tortula sinensis
288
Tortula muralis
288
Tortula andersonii
288
288
Tortula indet NSW
Tortula handelii
288
Tortula amphidiacea
288
Tortula subaristata
288
Tortula ruralis
Tortula caninervis
288
288
Tortula cavelii
288
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Unrooted Deep Green Phylogenetic
Network Occurance of Tr288 Orthologs
Riccia frostii
Riccia membranacea
Riccia albolimbata
Riccia sulivantii
Riccia atromarginata
Targionia
Riccia albida
Lunularia
Asterella
Probable Network Root
Lophocolea
Blasia
algal ancestor
Haplomitrium
Osmunda
Equisetum
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Angiopteris
Notothylas
Megaceros
Psilotum
288
Anthoceros
Sequoia
Anthoceros fusiformis
Selaginella
Sphagnum palustre
288
Huperzia
Sphagnum cuspidatum
Isoetes
Tetraphis
288
Polytrichum piliferum
Pterogonium
Buxbaumia
288
Polytrichum commune
Exostratum
Funaria
Octoblepharum
288
Grimmia
Leucophanes
288
Calyptopogon
Arthrocormus
Tortula ruralis
288
Mitthyridium
288
Tortula princeps
Tortula muralis
288
288
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Phylogenetic Approachto Functionality

• Establishment of a correlation between the
  presence of a gene and a specific phenotype
• Establishment of the role of a gene in the
  evolution of a particular phenotype
• Establishment of the importance of a particular
  mechanism in the evolution of a particular
  phenotype, e.g., induced repair upon rehydration
  versus induced protection during drying in
  desiccation-tolerance

Collaboration with Brent Mishler - UC Berkeley
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Deep change in function
A phylogenetically distant comparison large
background differences
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Recent Change in function
A phylogenetically close comparison low
background differences
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Increasing complexity
Ancestor-descendant comparison using reconstructed
ancestral states