Title : Cell type-specific expression patterns of heat shock protein AtHSP90-2 in Arabidopsis seedlings
Heat shock proteins are described to be molecular chaperones that promote protein folding and maintain cellular proteostasis in an organism under normal and stressful conditions. HSP90 family takes roles in many cellular processes through regulation of a diverse set of proteins involved in different signal pathways, cell growth and differentiation, plastic responses and control of heat shock response. However, there is an increasing number of data indicating cell type-specificity of HSP expression. AtHSP90-2 is a constitutive cytosolic member of the HSP90 family in Arabidopsis thaliana. Using a transgenic GUS line (Gene Trap collection, John Innes Center), we detected AtHSP90-2 promoter activity pattern in seedlings under normal conditions and abiotic impacts. Histological GUS assay during the first 12 days of seedling development showed dynamics of tissue specific AtHSP90-2 expression under normal conditions. In 12-day-old seedlings, GUS staining was detected in all organs, at high levels – in the vasculature, parenchyma, hydathodes and stipules of cotyledons and true leaves. However, variation of AtHSP90-2-GUS expression intensity between individuals, and even variegated cell type-specific patterns of GUS staining in hypocotyls and roots were observed. Such variability in HSP90 expression can obviously lead to differences of the basic tolerance between organisms. Under stressful conditions, changes in the intensity of AtHSP90-2-GUS expression with keeping the tissue-specificity were determined. High temperature (37°C, 2 h) resulted in an increase of GUS staining in all tissues that was corresponded to our RT-PCR data. Gradual dehydration of the nutrient medium led to an increase in the histochemical staining of the vasculature in the leaves as compared with other tissues. The findings suggest that the functioning of AtHSP90-2 has a certain tissue-specificity, which develops during the organ formation and is modulated by environmental conditions.