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Figure 1. 

Chromosomal distribution and circos diagram for the chromosomal distribution and interchromosomal relationships of Hsf genes in switchgrass. (a) The scale bar on the left indicates the length (Mb) of switchgrass chromosomes. (b) Gray lines indicate all synteny blocks in the switchgrass genome, and the red lines indicate duplicated Hsf gene pairs. The chromosome number is indicated at the center of each chromosome.

Figure 2. 

Unrooted phylogenetic tree of switchgrass, Arabidopsis, and rice Hsf proteins. The 97 Hsf proteins' alignments and unrooted phylogenetic tree was based on the Neighbor-joining method with 1,000 bootstrap replicates and P-distance method performed by MEGA 7.0. Hsf proteins of switchgrass, rice, and Arabidopsis are marked with green circles, triangles, and stars, respectively. The 15 distinct groups are divided by different circular arcs with the color of blue, red, and purple. Gene ID and amino acid sequences of AtHsfs and OsHsfs are shown in Supplementary Table S3.

Figure 3. 

Multiple sequence alignment of the DBD domains of Hsfs in switchgrass. The secondary structure elements of DBD (α1-β1-β2-α2-α3-β3-β4) are shown above the alignment. Rectangles represent α-helices and arrows represent β-sheets.

Figure 4. 

Phylogenetic relationship, exon-intron structure, and conserved motifs of the Hsf family in switchgrass.

Figure 5. 

The expression of PvHsf genes in different tissues, (a) organs, and (b) developmental stages in switchgrass. (a) Relative expression of PvHsf genes in floral organs days after pollination (DAP). (b) Relative expression of PvHsf genes in root, crown, node, leaf, leaf sheath, vascular tissues, stem, etc.

Figure 6. 

qRT-PCR analysis of the PvHsf gene expression in switchgrass leaves in response to (a) NaCl stress, (b) PEG stress, (c) ABA stress, and (d) CdCl₂ stress. The expression of PvHsfs was analyzed at 0, 1, 3, 6, 12, and 24 h under stress treatment.

Figure 7. 

Functional evaluation of PvHsfs in Cd-tolerance using Cd-sensitive yeast.

Figure 8. 

Subcellular localization of PvHsf16 and analysis of transgenic Arabidopsis over-expressing PvHsf16. (a) Subcellular localization of PvHsf16-GFP fusion protein in leaves of N. benthamiana. (b) Phenotypes of PvHsf16-overexpressed Arabidopsis (OE) lines under CdCl₂ stress. (c)−(e) Chl content, root length, and biomass of PvHsf16-OE lines under CdCl₂ stress. Data (n = 4) of transgenic lines marked with * in (c)−(e) represent significant difference at p ≤ 0.05 compared to WT under each treatment.