Mutation in Arabidopsis HIT1 locus causing heat and osmotic hypersensitivity

A mutant strain of Arabidopsis thaliana var. Columbia whose seedling develo pment was 2 to 3 degreesC more sensitive to high temperature inhibition tha n wild type was isolated. This mutant (hit1, for heat-intolerant) did not s how any phenotypic change when grown at 22 degreesC. However, incubation at 37 degreesC 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 be coming 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 man nitol (>300 mmol/L). These data imply that HIT1 may be responsible for wate r status regulation by which plants survive heat stress. Genetic analysis s hows that the hit1 phenotype is conditioned by a single recessive, nuclear mutation, and the HIT1 locus was closely linked to the nga280 microsatellit e marker on chromosome 1.