*3.7. Expression Profiles of Zea mays HSFs during Different Developmental Stages*

The expression patterns of *Zea mays* HSF genes were investigated during different growth stages and across different time scales. Although gene expression pattern is not always directly related to protein abundance, the transcriptome profiles can still provide insights into the probable role of genes in particular biological processes [69]. The transcriptome data utilized in the present study was downloaded from the maize genome database [59].

The *ZmHSF-04*, *ZmHSF-05*, and *ZmHSF-06* are shown to be the most highly induced HSFs across all the tissues during different growth stages (Figure 9A–C). During seed developmental stages, *ZmHSF-02*, *ZmHSF-03*, *ZmHSF-04*, *ZmHSF-07*, *ZmHSF-08*, *ZmHSF-09*, *ZmHSF-13*, *ZmHSF-15*, *ZmHSF-19*, *ZmHSF-20*, *ZmHSF-23*, and *ZmHSF-25* are upregulated (Figure 9A). A total of 8 HSFs showed very little or no expression at all. Interestingly, the transcripts of all ZmHSFs completely disappear 12 days after pollination. During vegetative stage, the *ZmHSF-01*, *ZmHSF-02*, *ZmHSF-09*, *ZmHSF-13*, *ZmHSF-14*, *ZmHSF-15*, *ZmHSF-19*, *ZmHSF-23*, and *ZmHSF-25* are upregulated (Figure 9B). This indicates that these genes might play putative regulate role in these tissues and control vegetative growth. *ZmHSF-22* and *ZmHSF-24* showed no expression during vegetative stage. The highest expression of ZmHSFs was observed in root tissues. Similarly, at reproductive stage across different tissues, *ZmHSF-02*, *ZmHSF-04*, *ZmHSF-13*, *ZmHSF-15*, *ZmHSF-19*, and *ZmHSF-25* are upregulated (Figure 9C). Interestingly, the transcripts of most HSFs except for *ZmHSF-02*, *ZmHSF-04*, *ZmHSF-05*, *ZmHSF-06*, *ZmHSF-16*, and *ZmHSF-25* completely disappear in pollen tissues. ZmHSF-17 showed almost no expression in any tissue during reproductive stage. Most of the HSFs were highly expressed in silk tissues.

**Figure 9.** *Cont*.

**Figure 9.** Expression profiles of maize HSFs in different seed (**A**), vegetative (**B**), and reproductive (**C**) tissues based on transcriptome data. The heat map was constructed using Tbtools. The color bar at the top right represents the log transformed FPKM values. Green represents higher, red lower, and yellow, medium transcript values.
