Poster: Ecophysiology

Abs # 14: Phylogenetic analyses in Cornus substantiate ancestry of xylem supercooling

Presenter:	Karlson, Dale T, dale.karlson@mail.wvu.edu
Authors	Karlson, Dale T (A) (C)  Xiang, (Jenny) Qiu-Yun  (B)   Stirm, Vicki E (C)   Shirazi, Abbas M (D)   Ashworth, Edward N (C)
Affiliations:	(A): West Virginia University (B): North Carolina State University (C): Purdue University (D): The Morton Arboretum
Web Site:	http://www.caf.wvu.edu/plsc/genetics/Karlson/

The response of wood to freezing temperature has evolved into two distinct behaviors; an avoidance strategy in which intracellular water supercools and a freeze-tolerance strategy where ice forms in extracellular spaces. Unlike supercooling, extracellular ice formation initiates the withdrawal of intracellular water and results in freeze-induced dehydration. Dehydrin proteins, which accumulate during cold acclimation in numerous herbaceous and woody plants, have been speculated to provide protection from desiccative extracellular ice formation. Here we use Cornus as a model system to provide the first phylogenetic characterization of xylem freezing behavior and dehydrin-like proteins. Our data suggest that both freezing behavior and the accumulation of dehydrin-like proteins in Cornus are lineage related; supercooling and non-accumulation of dehydrin-like proteins are ancestral within the genus. The non-supercooling strategy evolved within the blue- or white- fruited subgroup; where representative species exhibit high levels of freeze tolerance. Within the blue- or white- fruited lineage, a single origin of dehydrin-like proteins was documented and displayed a trend for size-increase in molecular weight. Phylogenetic analyses revealed that an early divergent group of red-fruited supercooling dogwoods lack a similar protein. Contrary to its speculated function, dehydrin-like proteins were neither limited to non-supercooling species nor to those that possess extreme freeze-tolerance.