Mediates both basal and acquired thermotolerance. Expressed in seedlings, leaves, stems, inflorescences and siliques. Target of TAS1 (trans-acting siRNA precursor 1)-derived small interfering RNAs in response to temperature variations. Up-regulated by cold (at 4 degrees Celsius), but rapid drop of expression after a temperature shift to room temperature (at 22 degrees Celsius) (PubMed:20622450). Highly up-regulated in seedlings exposed to heat shock (PubMed:24728648). Belongs to the heat induced plant HTT protein family.