31003:

The extremes of drought: understanding mechanisms of vegetative desiccation-tolerance.

Authors:	Oliver, Melvin, J.(A)O'Mahony, ()Velten, Jeff(A)
Affiliations:	(A): PSGD USDA-ARS
Presenter:	Oliver, Melvin J., moliver@mail.csrl.ars.usda.gov

Tortula ruralis is a plant capable of surviving the complete loss of water from its vegetative cells; the most extreme drought, viz: desiccation. Our earlier studies have produced a body of evidence that this plant achieves desiccation-tolerance by a mechanism that combines a constitutive level of cellular protection with a rehydration induced repair system. The rehydration induced repair and recovery process is facilitated by a change in gene expression that is mediated at the level of translation and, if drying is slow, utilizes mRNA that is stored in mRNPs formed during drying. The stored mRNAs encode a group of proteins whose synthesis, we postulate, is essential to the re-establishment of cellular integrity. We have named these proteins rehydrins, a nomenclature based on function rather than structure. We have cloned and sequenced a number of rehydrin cDNAs as well as a small but expanding desiccation/rehydration cDNA-EST database. Recent efforts have concentrated on three rehydrins; Tr155 encoding a putative alkyl-hydroperoxidase, Tr213 that encodes a plant polyubiquitin, and Tr288 that encodes a protein with no significant homology to any Genbank entry, yet has features similar to dehydrins. The predicted Tr288 protein contains 15 repeated motifs that are unrelated to Lea proteins yet it contains a single dehydrin K box segment at its carboxy end. The isolation of several independent Tr288 genomic clones has revealed that within Tortula populations the Tr288 gene contains variable numbers of the repeat motifs. We have transgenic tobacco that overexpress Tr288 and Tr155 and we are analyzing these plants for alterations in phenotype. Tr213 has been used to study the ubiquitin based protein turnover pathway and its response to desiccation and rehydration in both Tortula and a desiccation-tolerant angiosperm, Sporobolus stapfianus. We are presently attempting to establish a homologous recombination protocol for Tortula to enable us to study gene function and promoter properties of rehydrins via gene replacement.