Mutation in Arabidopsis HIT1 locus causing heat and osmotic hypersensitivity

A mutant strain of Arabidopsis thaliana var. Columbia whose seedling development was 2 to 3°C more sensitive to high temperature inhibition than wild type was isolated. This mutant (hit1, for heat-intolerant) did not show any phenotypic change when grown at 22 °C. However, incubation at 37 °C for 4 days was determined to be lethal for the mutant but not for wild-type plants. Leaves of wild type respond to high temperature by becoming erect, but by comparison leaves of the hit1 mutant remain horizontal and show a slightly wilty appearance. Furthermore, seedling development in hit1 mutants was more sensitive to osmotic stress imposed by exogenous mannitol (> 300 mmol/L). These data imply that HIT1 may be responsible for water status regulation by which plants survive heat stress. Genetic analysis shows that the hit1 phenotype is conditioned by a single recessive, nuclear mutation, and the HIT1 1ocus was closely linked to the nga280 microsatellite marker on chromosome 1.