Together with light, temperature is one of the major environmental cues regulating plant growth. In Arabidopsis thaliana, growth responses to high ambient temperature occur already in early stages of seedling development, hypocotyl elongation being one ofthe best characterized model phenotypes. At the molecular level, temperature-mediated plant morphology (also named thermomorphogenesis) is largely dependent on the transcription factor PHYTOCHROME INTERACTOR FACTOR 4 (PIF4). However, regulation of PIF4 onboth transcriptional and post-transcriptional level is very complex and remains rather poorly understood. To exploit both the phenotypic and genotypic variation observed and to identify novel components of the temperature signaling pathway, temperature-induced hypocotyl elongation (TIHE) was used as a model response to perform a QTL analysis in the Bay x Sha RIL population and an EMS-mutagenesis screen in the Rrs-7 ecotype. As a result, the circadian clock component EARLY FLOWERING 3 (ELF3) and the brassinosteroid transcription factor BRASSINAZOLE RESISTANT 1 (BZR1) are highlighted here as novel components by gating PIF4 in the control of thermomorphogenesis.