Desiccation Tolerance Mechanisms and Evolution Mel Oliver and Brent Mishler

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

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.

Desiccation-tolerant Plants.  Desiccation-tolerant  ALGAE  LICHENS  BRYOPHYTES  Modified Desiccation-tolerant  FERNS  ANGIOSPERMS

Distribution of Desiccation Tolerance in the Plant Kingdom liverworts hornworts mosses Selaginella Isoetes Lycopodium Equisetum ferns Gingko cycads conifers gnetophytes Angiosperms Land Plants Tracheophytes Seed Plants Oliver, Tuba and Mishler 2000

Tortula ruralis

Selaginella Selaginella bigelovii

Polypodium virginianum

Photo Courtesy of Dr Christina Walters USDA NSSL Fort Collins Orthodox Seeds

Distribution of Desiccation tolerance in the Angiosperms Poaceae Cyperaceae Velloziaceae Liliaceae Magnoliales renunculids Hamameliales Labiatae Gesneriaceae Scrophulariaceae Angiosperms Oliver, Tuba and Mishler 2000

Xerophyta villosa

Photo Courtesy of Dr. Jill Farrant and Clare Vander Willegen University of Cape Town SA Myrothamnus flabellifolia

Craterostigma wilmsii

Xerophyta viscosa

Sporobolus stapfianus

Photos Courtesy of Dr. Dorothea Bartels University of Bonn Craterostigma plantagineum Dry Rehydrated Hydrated

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

Essence of Desiccation-tolerance. Testable Hypothesis Cellular Repair Cellular Protection

Bryophyte Model Dry Rehydrated Hydrated RAPID WATER LOSS Constitutive Cellular Protection Protection Induction of Recovery and Repair Mechanisms Hormone ?

Angiosperm Model SLOW WATER LOSS Induction of Cellular Protection Re-establishmentProcesses Dry Rehydrated Hydrated ABA

Postulated Evolutionary History of Desiccation Tolerance in Land Plants hornworts mosses Selaginella Isoetes Lycopodium Equisetum ferns Gingko cycads conifers gnetophytes Angiosperms liverworts Constitutive protection and repair Inducible protection plus repair? Developmentally programmed protection - propagules Developmentally programmed protection - spores? Inducible protection (repair?) and later poikilochlorophylly T S Loss of vegetative desiccation tolerance in the ancestral lineage Oliver, Tuba and Mishler 2000

Bryophyte Model Dry Rehydrated Hydrated RAPID WATER LOSS Constitutive Cellular Protection Protection Induction of Recovery and Repair Mechanisms Hormone ?

ABCDEFGHIJKLMNO In 1 2 Dhy EFGH Tr 288 Phylogenetic Gene Search Tr 288 Gene GPN-Box Consensus primers Expected PCR Products (Sequence for Identity)

Tortula ruralis Tortula sinensis Tortula andersonii Tortula indet NSW Tortula amphidiacea Tortula subaristata Tortula caninervis Tortula cavelii Tortula handelii Tortula muralis Tortula papillosa Calyptopogon 288 Probable tree root Unrooted Tortula Phylogenetic Network Occurance of Tr288 Orthologs

Equisetum Osmunda Angiopteris Sequoia Selaginella Huperzia Isoetes Polytrichum piliferum Polytrichum commune Funaria Grimmia Tortula ruralis Tortula princeps Tortula muralis Arthrocormus Leucophanes Octoblepharum Exostratum Pterogonium Sphagnum cuspidatum Sphagnum palustre Anthoceros fusiformis Anthoceros Megaceros Notothylas Blasia Asterella Riccia albida Riccia atromarginata Riccia albolimbata Riccia frostii Riccia membranacea Riccia sulivantii Targionia Lunularia Lophocolea algal ancestor 288 Mitthyridium 288 Calyptopogon 288 Probable Network Root Psilotum Buxbaumia Tetraphis Haplomitrium Unrooted “Deep Green” Phylogenetic Network Occurance of Tr288 Orthologs

Phylogenetic Approach to 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

Deep change in function in function A phylogenetically distant comparison = large background differences

A phylogenetically close comparison = low background differences Recent Change in function in function

Increasing complexity Ancestor-descendant comparison using reconstructed ancestral states