The maize heat shock factor-binding protein paralogs EMP2 and HSBP2 interact non-redundantly with specific heat shock factors

Abstract

The heat shock response (HSR) is a conserved mechanism by which transcripts of heat shock protein (hsp) genes accumulate following mobilization of heat shock transcription factors (HSFs) in response to thermal stress. Studies in animals identified the heat shock factor-binding protein1 (HSBP1) that interacts with heat shock transcription factor1 (HSF1) during heat shock attenuation; overexpression analyses revealed that the coiled-coil protein HSBP1 functions as a negative regulator of the HSR. Zea mays contains two HSBP paralogs, EMP2 and HSBP2, which exhibit differential accumulation during the HSR and plant development. Embryo-lethal recessive emp2 mutations revealed that EMP2 is required for the down-regulation of hsp transcription during embryogenesis, whereas accumulation of HSBP2 is induced in seedlings following heat shock. Notwithstanding, no interaction has yet been demonstrated between a plant HSBP and a plant HSF. In this report 22 maize HSF isoforms are identified comprising three structural classes: HSF-A, HSF-B and HSF-C. Phylogenetic analysis of Arabidopsis, maize and rice HSFs reveals that at least nine ancestral HSF isoforms were present prior to the separation of monocot and eudicots, followed by differential amplification of HSF members in these lineages. Yeast two-hybrid analyses show that EMP2 and HSBP2 interact non-redundantly with specific HSF-A isoforms. Site-specific mutagenesis of HSBP2 reveals that interactions between hydrophobic residues within the coiled coil are required for HSF::HSBP2 binding; domain swapping demonstrate that the isoform specificity of HSF::HSBP interaction is conferred by residues outside of the coiled coil. These data suggest that the non-redundant functions of the maize HSBPs may be explained, at least in part, by the specificity of HSBP::HSF interactions during plant development.

Cytosol-Localized Heat Shock Factor-Binding Protein, AtHSBP, Functions as a Negative Regulator of Heat Shock Response by Translocation to the Nucleus and Is Required for Seed Development in Arabidopsis

“…Besides, the expression of heatinducible AtHSBP (Fig. 3A) was similar to that of ZmHSBP2 under thermal stress (Fu and Scanlon, 2004), and the roles of EMP2 and ZmHSBP2 in HSR were suggested to be nonredundant (Fu et al, 2006). These findings may support that one AtHSBP confers multiple functions required for embryo viability and regulation of the HSR.…”

“…Both ZmHSBP paralogs interact nonredundantly with specific HSFs, and this reveals that EMP2 and ZmHSBP2 may have distinct functions during plant development and HSR. However, the functions of ZmHSBP2 need to be clarified (Fu and Scanlon, 2004;Fu et al, 2006).…”

Common and Distinct Functions of Arabidopsis Class A1 and A2 Heat Shock Factors in Diverse Abiotic Stress Responses and Development

“…Genetic disruption of one HSF gene may not necessarily produce an obvious phenotype, as exemplified in recent studies of Arabidopsis A1-type HSFs (Lohmann et al, 2004;Liu et al, 2011;Nishizawa-Yokoi et al, 2011;Yoshida et al, 2011). Stable or transient overexpression of a HSF transgene may also generate misleading results, as the overexpressed protein may derepress the endogenous master HSFs by competing with the attenuators, such as HSP70, HSP90, and HSBP (Voellmy, 2004;Fu et al, 2006;Yamada et al, 2007;Hahn et al, 2011). For example, HSFA2 was shown to interact with HSP90 and HSBP (Meiri and Breiman, 2009;, and therefore overexpression of HSFA2 in the wild-type plant could derepress the HSFA1s, trigger a stress response, and enhance stress tolerance.…”

Identification and expression analysis of OsHsfs in rice

“…Molecular dissection of rice Hsf gene family would help to unravel the stress response mechanism in rice. Compared with the extensive studies done in Arabidopsis Hsf genes, only a few researches have involved monocots, such as rice and maize (Fu et al, 2006;Yamanouchi et al, 2002;Yokotani et al, 2008). Although 23 Hsfs were identified in the Oryza japonica previously, the structure and expression profile of these OsHsfs have not been elucidated.…”