Deep Evaluation to the Evolution History of Heat Shock Factor (HSF) Gene Family and Its Expansion Pattern in Seed Plants

Background: HSF (Heat shock factor) genes are essential in the irreplaceable functions in some of the basic developmental pathways in plants. Despite the extensive studies on the structure, function diversification, and evolution of HSF, their divergent history and gene duplication pattern remain unsolved. To further illustrate the probable divergent patterns in these subfamilies, we visited the evolutionary history of the HSF via phylogenetic reconstruction and genomic syntenic analyses by taking advantage of the increased sampling of genomic data for pteridophyta, gymnosperms and basal angiosperms. ResultsWe identified a novel clade including HSFA2, HSFA6, HSFA7, HSFA9 with complex relationship, very likely due to orthologous or paralogous genes retained after frequent gene duplication events. We suggested that HSFA9 was derived from HSFA2 through gene duplication in eudicots at ancestral state, and then expanded in a lineage-specific way. Our findings indicated that HSFB3 and HSFB5 emerged before the divergence of ancestral angiosperms, but were lost in common ancestors of monocots. We also presumed that HSFC2 was derived from HSFC1 in ancestral monocots. ConclusionThis work proposes that in the era of early differentiation of angiosperms during the radiation of flowering plants, the member size of HSF gene family was also being adjusted, accompanied with considerable sub- or neo-functionalization. The independent evolution of HSFs in eudicots and monocots, including lineage-specific gene duplication gave rise to a new gene in ancestral eudicots and monocots, and lineage-specific gene loss in ancestral monocots. Our analyses provide essential insights for studying evolution history of multigene family.