Identification and characterization of a heat-inducible ftsH gene from tomato (Lycopersicon esculentum Mill.)

A heat-inducible filamentation temperature-sensitive H (ftsH)-like gene was cloned from tomato leaves, and the deduced protein precursor was predicted to be targeted to the chloroplast. Because the protein structure was highly homologous to Arabidopsis AtFtsH6, the cloned tomato ftsH-like cDNA was named LeftsH6. It was characterized as heat-inducible and rapidly responsive to heat stress. However, no LeftsH6 expression was detected after cold, salt, drought or light stress challenges. Heat shock elements (HSEs) were identified in the 5′-flanking sequence of LeftsH6, which specifically bound heat shock factor (HSF) HsfA2 from tomato as determined by electrophoretic mobility shift assay (EMSA) analysis. Subsequently, transgenic tobacco plants carrying the β-glucuronidase (GUS) gene driven by the LeftsH6 promoter were generated. High levels of heat-induced GUS staining were detected in the leaves, roots and flowers of transgenic plants. The ovaries, stigmas, anthers and sepals in the flowers at various developmental stages, as well as the pollen grains of mature anthers, showed strong heat-induced GUS staining. In the leaves of transgenic tobacco, the highest level of fluorometric GUS activity was detected at 40 °C. These results showed that LeftsH6 is a typical heat shock gene and its thermoinducibility is mediated by interactions between HSEs of the LeftsH6 promoter and heat shock factor.