2011 Annual Report
1a.Objectives (from AD-416)
Elucidate the mechanism of dehydration tolerance in a model plant (fern) that differs in the level of tolerance between different life stages. The objective is to profile genes that respond to dehydration and rehydration and the degree of their expresssion, and to employ molecular phylogenomics to understand better how molecular mechanisms are related across green plants.
1b.Approach (from AD-416)
This work will examine species from three different habitats in Costa Rica: tropical dry forest, tropical lowland rain forest, and tropical high elevation paramo. Each site will be assessed and monitored for microclimate characteristics. Initial ecophysiological surveys of dessication tolerance (DT) will be made on field collected samples in Costa Rica. Others will be brought back to the US for detailed DT studies. At least for species from each habitat will be grown under controlled conditions. The DT capabilities for gametophytes and sporophytes for each species will be determined experimentally using controlled drying regimes coupled with survival assays and cell leakage measurements. The effect of dehyration on various physiological parameters (photosynthesis, respiration, water relations) will be assessed. Mechanisms of tolerance will be assessed by following the behavior of key cellular components during a wet-drywet cycle: including dehydrins (stress proteins), carbohydrates and key antioxidants. Dehydrins are of particular interest, as we will look at the gene structure, expression and protein accumulation patterns for each species. These measurements will form the basis of our molecular phylogenomics investigations.
This project is a collaborative effort between ARS and Colgate University and funded through the Harvey Picker Institute for Disciplinary Studies in the Sciences and Mathematics. This is the first year report. The primary objective of the project, for ARS, is to uncover the mechanisms by which different life stages of ferns survive desiccation. In doing so, we will uncover novel mechanisms for drought tolerance and address objective 2 of the parent project "Develop strategies and mechanisms for improving drought stress tolerance in maize." The ARS approach is to look at key genetic components of desiccation tolerance and to determine their regulation during dehydration under controlled drying conditions. Our initial studies were focused on isolating and characterizing dehydrin protein expression, both at the transcriptional and translational levels, in a number of ferns subjected to dehydration. After much work we focused our attention to the fern, Lomariopsis vestita, as it exhibits a unique expression of desiccation tolerance, going from tolerant to sensitive, as it transitions from an epiphytic to a terrestrial growth pattern. We considered the filmy ferns as a group as there are sister species within them that have different tolerance levels. We thoroughly explored the use of dehydrins as a marker of tolerance in these ferns and it has proven to be unsatisfactory on many levels. We recently moved to a different marker, the Early Light Inducible Protein (ELIP) gene family, which not only has shown great promise in this regard but also linked our work more closely to the ecophysiological and biochemical aspects of the project. The progress made was exactly as outlined for the ARS portion of the project and we made significant inroads into understanding how desiccation tolerance is regulated in plants. These studies will ultimately identify the regulation and genetic components of the complex phenotype of drought tolerance and its improvement in crops.