Melvin Oliver

USDA-ARS, Lubbock; and Texas Technological University

The major focus of the research in my laboratory is to gain an understanding of the basic mechanisms involved in desiccation-tolerance of plant tissues (both vegetative and propagative) and to isolate and characterize the genes that are of fundamental importance in this complex plant phenotype. Much of my work has been devoted to understanding the mechanism of vegetative desiccation tolerance exhibited by the desiccation tolerant bryophyte Tortula ruralis. I have established over the years that this less complex plant utilizes constitutive cellular protection bolstered by a rehydration induced cellular repair component to generate vegetative desiccation tolerance (see reviews Oliver 1996, Oliver and Bewley, 1997). Some of our more recent work has lead to the discovery that transcripts required for recovery following rehydration, coding for a group of proteins we have designated as rehydrins (Oliver 1991), accumulate in mRNP particles during the drying process (Wood and Oliver, 1999). We have used a cDNA library derived from these stored mRNAs to establish a small but expanding Tortula EST database (Wood et al, 1999). Conventional differential screening of Tortula libraries and information gleaned from our EST database have enabled us to look at several genes that may play key roles in desiccation tolerance or lead us to those processes that are of import. We have also, in collaboration with an Australian group headed by Don Gaff and John Hamill at Monash University, entered into a study into the molecular aspects of vegetative desiccation tolerance in the South African grass Sporobolus stapfianus. We have established a role for a desiccation responsive small GTP binding protein (Rab2) that is involved in membrane vesicle traffiking in both the drying and recovery phases (O'Mahony and Oliver, 1999). Some of our more recent work has focused on a comparison between the mechanisms of tolerance in Tortula and in Sporobolus especialy in the areas of protein protein and RNA turnover (O'Mahony and Oliver, 2000, and In Press).

Our present focus in the lab has centered on two interrelated lines of investigation that have developed out of our overall understanding of the evolution of desiccation tolerance in land plants (these views are given in the body of the RCN proposal and are in Oliver, Mishler and Tuba 2000).. The first line of investigation involves the use of technologies developed for plant genomics to identify genes that are central to all mechanisms of desiccation tolerance in plants and genes that are unique to each of the three major mechanisms. To do this we are preparing cDNA microarrays derived from transcripts involved in the desiccation induced responses of; 1. Tortula ruralis representing constitutive cellular protection and rehydration induced repair, 2. Arabidopsis seeds representing developmentally programmed established cellular protection, and 3. Sporobolus stapfianus representing the more recent environmentally induced cellular protection mechanism. Analysis of these microarrays should yield a wealth of data and genes that can be used in comparative analyses designed to take advantage of the information generated by Deep Green. In addition to the simple isolation of genes involved in desiccation tolerance, we are developing the unique capability of directly assessing their function in a tolerant system (Tortula ruralis) by the use of homologous recombination, a system that has proved useful in other bryophyte models. Our second line of investigation involves the identification of "homologs" of the genes we have identified as important in desiccation tolerance (mainly from T. ruralis) in closely related species and in the "Exemplar species" as defined by "Deep Green". In this way we hope to establish a correlation between the presence of a gene and the presence of desiccation tolerance and to gain an insight into the role of specific genes in the evolution of this trait. Such information may also provide data to support (or not) our hypotheses concerning the importance of particular mechanisms in the evolution of a desiccation-tolerance. We have already established a collaboration with members of Deep Green, in particular Brent Mishler and his group, so the RCN proposal would help us to broaden this interaction and perhaps complement studies of a similar trend in other labs. We also hope to gain a great deal from a stronger association with those labs that are actively involved in genomic level studies to help us integrate our more narrow focus on a genomic approach to one particular phenotype into the much broader scope of plant genome analysis.