Heat Shock Genes - Thermal stress induces the transcription of a small set of heat shock genes in diverse organisms, and also reduces the expression of many other vital genes. The upstream region, of heat shock genes regulating their expression is highly conserved.

Thus, when a gene construct, carrying NPT II reporter gene, fused with upstream region of heat shock gene hsp70 from Drosophila, was introduced into tobacco, induction of NPT II expression due to heat shock was comparable to that of endogenous plant heat shock genes (inducible in all organs except pollen).

Similarly, from maize a homologue of above gene, hsp70 with 1.1 kilobases of upstream sequence, when introduced in petunia exhibited heat inducibility.