Thermo-induced transcripts of a soybean heat shock gene after transfer into sunflower using a Ti plasmid vector.

A genomic DNA fragment containing a soybean heat shock gene (hs6871) was inserted into the T-DNA region of the Agrobacterium tumefaciens pTiC58 plasmid. A strain carrying the modified Ti plasmid was used to incite tumors in sunflower hypocotyls. The expression of the heat shock gene was investigated by Northern blot analysis of RNA and S1 nuclease mapping of the transcriptional start site. Heat shock-induced poly(A) mRNA was detected in tumor tissue only after incubation at 40 degrees C (heat shock) not at the normal growth temperature (28 degrees C). Transcripts from hs6871 are faithfully initiated in sunflower, starting at the same site on the DNA as in soybean. The low level of transcripts initiating correctly on hs6871 in sunflower is consistent with a general tissue-specific reduction in the expression of partially homologous native heat shock genes in sunflower tumors.