2.5. Epigenetic regulation of thermomorphogenesis
In a screen for mutants with enhanced temperature response, Kumar & Wigge (2010) discovered ARP6, a component of a chromatin remodelling complex. Mutants lacking ARP6 show constitutive warm temperature phenotypes. ARP6 is required for the deposition of a specific histone variant H2A.Z. It was shown that at warm temperatures, there is a reduction in H2A.Z occupancy at the promoters of warm-temperature induced genes and it was initially proposed that H2A.Z could play a role in temperature sensing (Kumar & Wigge, 2010). More recent evidence has however cast doubt on this hypothesis. It was shown that at warm temperatures, the binding of HSFA1a to heat responsive genes precedes the H2A.Z eviction and the activation of transcription (Cortijo et al., 2017). The eviction of H2A.Z is facilitated by HISTONE DEACETYLASE 9 (HDAC9), and is required for the full transcriptional response to elevated temperatures (van der Woude et al., 2019), but it appears that this occurs mostly downstream of temperature perception.