Daytime temperature is sensed by phytochrome B in Arabidopsis through a transcriptional activator HEMERA

Yongjian Qiu,Meng Chen,Carisha M Moore,Ruth Jean-Ae Kim,Meina Li

doi:10.1038/s41467-018-08059-z

Yongjian Qiu, Meng Chen + Show 3 more

Open Access

https://doi.org/10.1038/s41467-018-08059-z

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Abstract

Ambient temperature sensing by phytochrome B (PHYB) in Arabidopsis is thought to operate mainly at night. Here we show that PHYB plays an equally critical role in temperature sensing during the daytime. In daytime thermosensing, PHYB signals primarily through the temperature-responsive transcriptional regulator PIF4, which requires the transcriptional activator HEMERA (HMR). HMR does not regulate PIF4 transcription, instead, it interacts directly with PIF4, to activate the thermoresponsive growth-relevant genes and promote warm-temperature-dependent PIF4 accumulation. A missense allele hmr-22, which carries a loss-of-function D516N mutation in HMR’s transcriptional activation domain, fails to induce the thermoresponsive genes and PIF4 accumulation. Both defects of hmr-22 could be rescued by expressing a HMR22 mutant protein fused with the transcriptional activation domain of VP16, suggesting a causal relationship between HMR-mediated activation of PIF4 target-genes and PIF4 accumulation. Together, this study reveals a daytime PHYB-mediated thermosensing mechanism, in which HMR acts as a necessary activator for PIF4-dependent induction of temperature-responsive genes and PIF4 accumulation.

Highlights

Ambient temperature sensing by phytochrome B (PHYB) in Arabidopsis is thought to operate mainly at night
This study reveals a novel PHYB-mediated temperature-signaling mechanism, in which HMR acts as an essential transcriptional activator to induce the expression of growth-relevant PIF4 target genes and PIF4 accumulation in warm temperatures
The first step toward understanding PHYB’s role in thermosensing under LD or continuous light conditions is to determine an optimal plant growth condition that elicits a significant response to warm temperatures

Summary

Introduction

Ambient temperature sensing by phytochrome B (PHYB) in Arabidopsis is thought to operate mainly at night. This study reveals a daytime PHYB-mediated thermosensing mechanism, in which HMR acts as a necessary activator for PIF4-dependent induction of temperature-responsive genes and PIF4 accumulation. In accordance with the contrast in daylength-dependent rhythmic growth patterns, hypocotyl elongation is modulated by temperature changes at the distinct times in either the dark or light under SD and LD conditions, respectively[18]. Increases in temperature between 10 °C and 30 °C accelerate the darkreversion rate of PHYB, leading to a reduction of the steadystate level of the active Pfr form[19]. This temperature-dependent biophysical property makes PHYB a thermosensor for ambient growth temperatures[19,20]

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