Submitted to: Plant Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 11, 1998
Publication Date: N/A
Interpretive Summary: This paper represents part of a study focused on identifying genes involved in desiccation tolerance in plants, specifically the desiccation tolerant South African grass Sporobolus stapfianus. This grass has the ability to survive water loss to the level of air dryness, and even after extended periods in the desiccated state return to normal growth once water has been nre-introduced. Studies on desiccation tolerance mechanisms in plants sug- gest that such plants must be able to implement cellular protection mechan- isms to limit damage during water influx. Our research focuses on the re- hydration period where re-introduction of water may prompt the cell to mo- bilize its repair machinery. Here we report on a regulatory protein, Rab2, an integral part of the cullular apparatus required for transporting newly synthesized proteins and membranes to their correct locations. We have characterized the grass Rab2 gene and protein and show how its expression is regulated during drying and rehydration. Our report shows that the in- crease in Rab2 levels also occurs in a desiccation sensitive grass, sug- gesting it is not a trait exclusive to desiccation tolerant grasses. While the precise function of this protein is unclear, it seems from our results that it is required by this grass in greater amounts during drying and re- hydration. It may be part of a protective and/or repair mechanism necessary to allow the plant to survive desiccation, but further investigations are necessary to elucidate its role in this process.
Technical Abstract: The South African grass Sporobolus stapfianus is a modified desiccation tolerant plant in that it can survive desiccation only if dehydration is relatively slow. This plant is the model in our studies to identify genes critical to desiccation tolerance. Differential display was used to detect gene transcript modulation during dehydration and rehydration in leaves of Sporobolus stapfianus. A 291 bp RT-PCR product was isolated and confirmed by northern analysis to be differentially expressed. This RT-PCR product was used to isolate a full length cDNA encoding a polypeptide of 210 amino acids with an apparent molecular weight of 26.5 kD. Sequence similarity searches show this cDNA, and predicted protein, to be similar to the Rab2 from mammalian and plant sources. GTP interactive motifs and a C-terminal isoprenylation site in the deduced protein sequence indicate it is a membrane attached GTP binding protein. Rab2 proteins in animal systems are located in an intermediate compartment between the ER and golgi and involved with vesicle trafficking. Northern analysis indicates that in S. stapfianus Rab2 transcript was present at basal levels in nonstressed plants, accumulated throughout drying and again briefly during rehydration. Rab2 transcript was also present in leaves of the desiccation tolerant S. pellucidus and the desiccation sensitive S. pyramidalis, accumulating in both during drying and in S. pellucidus during rehydration. These results demonstrate that Rab2 expression is responsive to water stress in Sporobolus, but is not specific to desiccation tolerant plants. This suggests that Rab2, while required for cell maintenance, may have a role in desiccation/rehydration induced cellular repair.