Transcriptional Profiling Reveals a Time-of-Day-Specific Role of REVEILLE 4/8 in Regulating the First Wave of Heat Shock–Induced Gene Expression in Arabidopsis

Abstract

Although much is known about plant responses to heat shock (HS), how plants sense high temperature and the primary HS signal transduction pathway leading to HS-regulated gene expression are still poorly understood. To identify primary transcription factors that mediate HS-regulated gene expression and their target genes, RNA sequencing was performed to detect genes whose expression is rapidly altered by HS in Arabidopsis (Arabidopsis thaliana). The results showed several genes were induced after only 5 min of HS treatment, suggesting that HS signaling occurs very rapidly. Analysis of the ciselements in the promoters of genes upregulated by 10 min of HS treatment identified HEAT SHOCK FACTOR A1s (HSFA1s) and circadian clock proteins REVEILLE4 (RVE4) and RVE8 as essential transcription factors that independently mediate early HS-induced gene expression. Using hsfa1a/b/d/e and rve4/8 mutants, we identified subsets of HSFA1s-or RVE4/8dependent early HS-induced genes and showed RVE4/8 regulate plant thermotolerance partially by regulating the expression of downstream transcription factors ETHYLENE RESPONSIVE FACTOR53 (ERF53) and ERF54, specifically around noon. These findings reveal a potential transcriptional regulatory hierarchy governing the first wave of HS-induced gene expression. They also provided important insight into the mechanism by which the circadian clock gates thermotolerance and prepares plants for exposure to high temperatures during the day.

Specific functions for Mediator complex subunits from different modules in the transcriptional response of Arabidopsis thaliana to abiotic stress

“…Interestingly, eight of these (LHY, CCA1, and RVE1, 3, 4, 5, 6, 8) belong to a subgroup of 11 Myb-related TFs primarily associated with circadian clock functions 68 . However, LHY, CCA1, and RVE4/8 have also been identified as key regulators of abiotic stress responses 69,70 .…”

Interaction between the Circadian Clock and Regulators of Heat Stress Responses in Plants

“…Emerging transcriptome studies suggest that during the day, the plant transcriptional response to heat stress is quite dynamic [50,59]. In Arabidopsis, the transcript abundance of clock genes is altered in response to heat stress depending on the time of day [50] ( Figure 2).…”

“…Together, HSFs are expressed throughout the day (morning, afternoon, and evening), with at least one HSF showing timing of peak expression (phase) every 4 h (Figure 3) [29,81]. Although not all HSFs respond to heat stress, this TF family plays a role in other abiotic stress responses [50,59,[81][82][83]. The observation that they are available at almost all time points during the day supports an important functional role of HSFs in the plant response to external stress signals, which is most likely mediated by the clock.…”

“…HSFA1e, A3, A4a, A6b, A8, B2aI, and C1 are direct targets of clock genes based on chromatin immunoprecipitation followed by deep sequencing (ChIP-seq); however, experimental evidence to link the biological significance of these interactions needs to be further examined [84][85][86][87][88]. Interestingly, one of the HSFs (HSFB2b) has been shown to play a role in the clock's ability to buffer against certain temperature changes, suggesting a feedback regulatory A B Although not all HSFs respond to heat stress, this TF family plays a role in other abiotic stress responses [50,59,[81][82][83]. The observation that they are available at almost all time points during the day supports an important functional role of HSFs in the plant response to external stress signals, which is most likely mediated by the clock.…”

Development and Application of a PCR-Based Molecular Marker for the Identification of High Temperature Tolerant Cabbage (Brassica oleracea var. capitata) Genotypes

“…To cope with heat stress, plants rapidly (within 10 min) induce the expression of heat stress-responsive genes (HSRs) through various signaling pathways, such as the phytochrome B-and phytochrome-interacting factor 4 (PIF4)-dependent pathway [9,10], cyclic nucleotide-gated channels (CNGC)-calcium-calmodulin pathway [11][12][13], proteolytic cleavage-activated transcriptional activation pathway [14,15], ROS-induced pathway [4,16], and H2A.Z-related pathway [17]. Two different groups of transcription factors, including HEAT SHOCK FACTOR A1s (HSFA1s) and circadian clock proteins REVEILLE4/8 (RVE4/8), mediate early HSR expression through HSF-dependent and -independent pathways, respectively [18].…”