Identification of genetic diversity and mutations in higher plant acquired thermotolerance

Plants experience high air and soil temperatures during periods of drought and when fields receive limited irrigation. Elevated plant temperatures that occur under these conditions negatively impact plant health and productivity. Plants, like all organisms, respond to an elevation in temperature by the synthesis of heat shock proteins (HSP). The appearance of plant HSP is strongly correlated to the development of a condition termed 'acquired thermotolerance'. Acquired thermotolerance is induced by pre-exposure to elevated but non-lethal temperatures and leads to enhanced protection of plant cells from subsequent heat induced injury. Although the correlation between the development of acquired thermotolerance and the appearance of HSP is strong, a cause-and-effect relationship between the two has been difficult to demonstrate. To understand the relationship between HSP and acquired thermotolerance, mutations would be required that result in a coordinate change in the expressions of HSP. This paper describes research efforts leading to the development of a screening procedure for the isolation and characterization of acquired thermotolerance mutants. This method for identifying mutants is based on the inhibition of chlorophyll accumulation in etiolated tissue following challenges at lethal temperatures and the prevention of this inhibition by pre-incubation at a non-lethal elevated temperature; i.e. acquired thermotolerance. Arabidopsis thaliana mutants deficient in varying levels of acquired thermotolerance have been identified from both the RLD and Columbia ecotypes and these mutants are currently undergoing a detailed characterization at both the protein and molecular levels.