###### Abstract
Since the first plant HSF isolation from _Solanum Lyopersicum_ in the 1990s [7], many HSFs have been identified and characterized [8]. For instance, there are 21 HSFs in _Arabidopsis_, 25 in _Oryza sativa_, 31 in _Zea may_ ssp. _mays_, 38 in _Glycine max_ and 56 in wheat, divided into classes A, B and C based on their conserved domain structures [6; 9; 10; 11; 12; 13; 14; 15]. Most of the previous research focused on class A HSFs, which generally regulate the transcriptional activities of the genes involved in different environmental stress responses and the seed development process [16; 17; 18; 19; 20]. The class B family members do not contain insertions into the HR-A/B domain, while class A has 21 amino acid insertions and class C contains 7 amino acid insertions and class B HSFs generally lack the AHA motif in the C-terminal domain [21; 22], which is essential for transcriptional activity. Thus, some Class B HSFs do not show transcriptional activity or act as the co-activator by interacting with class A HSFs and generally suppress the activation of downstream stress-inducible genes [5]. For instance, _HSFB1_ of a tomato acts as a co-activator along with _HSFB1_ and modulates the expression activity of certain housekeeping and viral genes under high-temperature stress [23; 24]. In _Arabidopsis_, the _HSFB1_ and the _HSFB2b_ have already been reported to negatively control the expression of many stress-inducible genes (HSFs), including _HSFA2_, _HSFA7a_, _HSFB1_, _HSFB2b_ and Vin3, along with several other heat shock transcription factors [25; 26]. In _Arabidopsis_, the single and double mutants of the _HSFb1_ and the _HSFb2b_ significantly enhance the tolerance of Arabidopsis against abiotic stress tolerance [27]. In a previous transcriptome analysis of white clover under drought stress conditions, it was perceived that a transcription factor homolog to _HSFB2_ of Chickpea showed a stronger expression under drought stress [28]. The economically important forage, white clover, is vulnerable to abiotic stresses, adversely affecting its normal biological and physiological activities and interrupting fundamental cellular structures [29; 30]. Therefore, it is important to continuously explore effective means and resources to improve white clover's biotic and abiotic stress tolerance. Previously, we explored the physiological, transcriptomic and metabolomics responses of white clover under drought stress conditions and found highly differential expressions of the HSFB2 homolog [28]. To assist a strategy for the molecular improvement of white clover and broaden the understanding of how heat shock transcriptional factor and heat shock proteins modulate stress responses in white clover, we isolated and characterized a class B heat shock transcription factor HSFB2 from white clover cDNA and named it as _TrhSFB2a_ based on conserved domains characteristics. The qRT-PCR method was employed to investigate the spatial and temporal expression of _TrhSFB2a_ under different stress conditions. Furthermore, we synthesized overexpression _Arabidopsis_ and compared it with wild-type and T-DNA lines of _Arabidopsis_ in which the homolog of _TrhSFB2a_ was silenced by RNA interference (RNAii) to determine how HSFB2a protein responds under drought, heat and salt stress conditions. The current study results would improve the understanding of the molecular mechanism of the responses to extreme environmental conditions in white clover and explore the regulatory role of HSFs during ecological stress responses in plants.