AtHSBP functions in seed development and the motif is required for subcellular localization and interaction with AtHSFs.

In Arabidopsis thaliana, heat shock factor binding protein (AtHSBP) is a negative regulator of the heat shock response (HSR), and defective AtHSBP leads to seed abortion. We found that the wild-type and AtHSBP-knockout plants did not differ in ovule phenotypes at flower position 3, which indicates that the seed abortion occurs after fertilization and during embryogenesis. The conserved residues of the hydrophobic heptad repeat (HR) domains in AtHSBP were mutated and examined for their subcellular localization and interacting ability with heat shock factors (AtHSFs). The HR domains at the C terminus of AtHSBP are important for retaining AtHSBP in the cytoplasm under normal growth conditions and for interacting with AtHSFs, which negatively affects the DNA-binding capacity and transactivation activity of AtHSFs during the HSR.