Neighbor-joining phylogenetic tree of the Hsf members. The phylogenetic tree, constructed with MEGA4.0, has been generated on the basis of the amino acid sequences of the N-terminal domains of Hsfs including the DNA-binding domain, the HR-A/B region and parts of the linker between both two regions. ScHsf1 was set as the outgroup. Hsf proteins are divided into twelve groups (A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, B, C) based on previous research  and high bootstrap values (>50). The contents in brackets are corresponding Hsf annotations. Branches of members belonging to class A subclasses are represented by black lines, branches of members belonging to class B are represented with blue lines, and branches of members belonging to class C are represented with red lines. The abbreviations of species names are as follows: Zm, Zea mays; Os, Oryza; At, Arabidopsis thaliana.