OLIVER, MELVIN J.1*, JOHN A. WHEELER2, BRENT D. MISHLER3, and JEFF VELTEN1. 1USDA-ARS Plant Stress and Water Conservation Laboratory, 3810 4th StLubbock, TX 79415; 2Department of Biology, University of Wisconsin-River Falls 410 South Third Street, River Falls, WI 54022-5001; 3University Herbarium, Jepson Herbarium, and Department of Integrative Biology, University of California, Berkeley, CA 94720. - A bryophyte rehydrin trackable marker for the evolution of desiccation tolerance.
The use of phylogenetic data to address the importance of individual
genes in a complex phenotype or in the evolution of a particular
trait, is an approach that has received little attention. In
collaboration with The Green Plant Phylogeny Research Coordination
Group ("Deep Green"), we have initiated a study of the
evolution of desiccation tolerance. Phylogenetic analyses suggest that
desiccation tolerance was primitively present in the bryophytes
(basal-most living clades of land plants), but was lost early in the
evolution of tracheophytes. Desiccation tolerance has re-evolved in
seeds and pollen and vegetatively in Selaginella, the ferns, and at
least eight independent evolutions in the angiosperms. In the moss
Tortula ruralis, we have identified several genes that appear
to be intimately involved in desiccation tolerance. One of these
genes, a rehydrin Tr 288, accumulates transcript at high levels in
response to desiccation that are only used upon rehydration. This gene
has physical properties similar to the stress induced dehydrin
proteins. Tr 288 however, has little sequence similarity with
dehydrins other than the presence of a rudimentary K-box sequence at
its carboxy terminus. Our working hypothesis is that Tr288 is an
ancestral dehydrin and as such may be a useful marker in a
phylogenetic analysis of desiccation tolerance. We have devised a PCR
based strategy, utilizing the highly repetitive nature of Tr288, to
track the presence of Tr288 homologs in other species. Our studies
indicate that we can find homologs within the Tortula ruralis complex
and we are now expanding into other bryophyte groups and into the
tracheophyte lineages. In particular we will be targeting the exemplar
species identified by Deep Green in their synthesis of a phylogenetic
tree for all land plants.
Key words: Tortula ruralis , bryophytes, desiccation tolerance, rehydrin, stress biology