Expression analysis of PtHsp90 genes in different tissues. A. Heat map showing hierarchical clustering of PtHsp90 genes in vegetative tissues (YL, young leaves; ML, mature leaves; PS, primary stem; SS, secondary stem; R, roots). The data was obtained from our unpublished RNA-seq data. The expression level of genes was determined based on the value of RPKM (reads per kilobase of exon region in a gene per million mapped reads). Details of the RPKM are shown in Additional file 11. Color scale represents log2 expression values. B. Expression of seven selected PtHsp90s was quantified by quantitative reverse-transcription polymerase chain reaction (qRT-PCR) in vegetative tissues (ML, mature leaves; SS, secondary stem; R, roots). The average expression of each gene was calculated relatively to the first biological replicate of roots ± standard error (SE) (n≥3).