Constitutive transcription of a soybean heat-shock gene by a cauliflower mosaic virus promoter in transgenic tobacco plants

Transcription of heat‐shock protein genes in soybean can be induced by high temperature stress leading to a transient expression of heat‐shock proteins. We have tested whether the replacement of a native heat‐shock promoter by a viral promoter results in constitutive transcript levels of the respective gene in transgenic plants. The 35S‐transcript promoter of the cauliflower mosaic virus was linked to the protein‐coding region of the genomic heat‐shock gene hs6831, encoding a 17.6‐kD heat‐shock protein of soybean. After transformation of tobacco plants with this chimeric construction using a disarmed Agrobacterium binary vector, abundant mRNA levels were detected in transgenic plants. The steady‐state level of this mRNA at 25°C was equal to that generated by the native heat‐shock promoter at 40°C; however, it was markedly reduced by heat shock applied to the transgenic plants. These findings suggest a sufficiently high stability of heat‐shock mRNA produced at the normal growth temperature to direct constitutive expression of heat‐shock proteins. The application of constitutive gene expression for the investigation of thermotolerance is discussed.