Isolation and analysis of the expression of two genes for the 81-kilodalton heat-shock proteins from Arabidopsis.

We have cloned and characterized two members of the family of genes for the 81-kilodalton heat-shock proteins from Arabidopsis thaliana, HSP81-1 and HSP81-2. Comparison of the entire genomic sequence of the HSP81-1 gene with the corresponding full-length cDNA previously reported as AtHS83 (TW Conner, PR LaFayette, RT Nagao, JL Key [1990] Plant Physiol 94: 1689-1695) reveals the presence of three introns of 315, 83, and 88 base pairs. By contrast, analysis of the HSP81-2 genomic and partial cDNA sequences suggests that the HSP81-2 gene is interrupted by only two introns of 304 and 106 base pairs. The 5'-initiation sites of the two corresponding mRNAs were mapped from results of experiments with S1 nuclease. The deduced amino acid sequences of the proteins encoded by these two genes show 88% identity, and they also show striking similarities to the hsp90 family of proteins in yeast and animal cells. From the results of northern blot analysis of transcripts, it appears that the expression of the HSP81-1 gene occurs at only very low levels in the absence of heat shock and is strongly induced by heat (35 degrees C). The HSP81-2 gene is constitutively expressed at much higher levels, and its expression is moderately enhanced by elevated temperatures. Severe heat shock appears to block the splicing of the pre-mRNA transcribed from HSP81-1. We also examined the effects of arsenite and cadmium on the expression of the HSP81 genes, as well as on other groups of hsp genes in Arabidopsis. Treatment with cadmium was marginally effective in inducing hsp genes, whereas arsenite stress strongly stimulated the accumulation of each mRNA in a coordinated fashion.