Table 1.

Signaling processes and pathways involved in thermotolerance.

Gene	Species	Main Results	References
HSR (heat stress response) -mediated transcriptional processes
HSF1	Human	HSP (heat shock protein) 70 and the cochaperone Hdj1 interact directly with the transactivation domain of HSF (heat shock transcription factor) 1 and repress heat shock gene transcription	[23]
HSF1, HSF2	Human	Activation of HSF1 and HSF2 including the formation of trimers concomitant with the acquisition of DNA-binding activity and nuclear localization	[24]
HSF family	Multiple	Survey of Arabidopsis, rice and maize HSFs, sequence, structure and domain analysis	[27,28,29,30,31,32,33]
HSFA1s, HSFA2	Arabidopsis	HSFA1d and HSFA1e involved in the transcriptional regulation of HSFA2 function as key regulators for the HSF signaling	[34]
HSFA2	Arabidopsis	HSFA2 function as key regulators of HSF signaling, HSFA2 expression levels, heat stress responses and thermotolerance	[34,35,36,37,38,39]
HSFA6b	Arabidopsis	HSFA6b connects ABA (abscisic acid) signaling and ABA-mediated heat responses, contributes to thermotolerance, drought and salt tolerance	[40]
HSFBs	Arabidopsis	Heat-inducible expression of HSFB1, HSFB2A, and HSFB2B and the repressor activity of HSFBs	[41,42]
HSPs	Maize	HSPs response to heat stress in maize	[43,44,45,46,47,48]
UPR-mediated transcriptional processes
bZIP28	Arabidopsis	bZIP (basic leucine zipper) 28 contributes to the upregulation of heat-responsive genes and heat tolerance	[49]
bZIP28, bZIP60	Arabidopsis	bzip28 bzip60 double-mutant plants are sensitive to heat stress; bZIP28 binds directly to the promoters of heat-responsive genes	[50]
IRE1	Arabidopsis	Heat induces the splicing of bZIP60 by IRE1 (inositol-requiring enzyme 1); IRE1 confers heat stress tolerance, and this is attributable to its RNase domain	[51,52]
bZIP60, HSFTF13, HSPs	Maize	Maize heat stress response; bZIP60 links the UPR (unfolded protein response) to the HSR in maize by direct binding bZIP60 to the promoter of Hsftf13 to active its expression	[14]
bZIP60	Maize	bZIP60 expression levels in tropical and temperate maize lines with different heat tolerances	[53]
Others transcriptional processes
ABA/ calcium/ SA/ethylene, etc.	Arabidopsis, maize	The involvement of calcium, ABA, ethylene, and SA (salicylic acid) in protecting against heat-induced oxidative damage in Arabidopsis or maize.	[54,55,56,57]
HSFA2c, HSPs, ABA	Tall Fescue, Arabidopsis	FaDREB (dehydration-responsive element-binding protein) 2, FaAREB3 directly bind to DRE/ABRE cis-elements in the FaHSF2c promoter to drive expression and improve heat tolerance in Tall Fescue and Arabidopsis	[58]
ERF1/JA/ ethylene	Arabidopsis	ERF (ETHYLENE RESPONSE FACTOR) 1 activates target genes by binding to GCC boxes or DRE/CRT elements in HSFA3 and HSP70, and enhances tolerance to heat and other abiotic stresses.	[59]
JA/AOS/ ROS	Arabidopsis	JA (jasmonic acid) and ROS (reactive oxygen species) are required for plant acclimation to a combination of high light and heat stress, at both local and systemic level	[60,61]
DREB2A	Arabidopsis	Thermotolerance was significantly increased in plants overexpressing DREB2A CA and decreased in DREB2A knockout plants	[62]
DREB2A/ NF-YC10	Arabidopsis	As a DREB2A interactor, NF-YC10 (NUCLEAR FACTOR Y, SUBUNIT C 10) formed a transcriptional complex with NF-YA and NF-YB subunits, and the trimer enhanced heat stress-inducible gene expression in conjunction with DREB2A	[63]
NF-YC10/ GAPC	Arabidopsis	GAPC (glyceraldehyde-3-phosphate dehydrogenase) enters the nucleus in response to heat where it binds to NF- YC10 to increase the expression of heat-inducible genes, rendering Arabidopsis tolerant to heat stress.	[64]
SPL1, SPL12	Arabidopsis	SPL (SQUAMOSA PROMOTER BINDING PROTEIN-LIKE) 1 and SPL12 act redundantly to enhance thermotolerance through PYL-mediated ABA signaling in Arabidopsis	[65]
SDG25, ATX1	Arabidopsis	Histone H3K4 methyltransferases SDG25 and ATX1 regulate histone H3K4me3 level and prevent DNA methylation at loci associated with heat stress gene expression during stress recovery	[66]
APX1, 2	Arabidopsis	HSF21 is key in the early sensing of H2O2 stress in KO-Apx1 (ascorbate peroxidase 1) plants. Increased H2O2 production during the early phase of heat stress is necessary for the HSFs-mediated induction of HSP17.6 and HSP18.2	[67,68,69]
Post-transcriptional processes
AS, SR45a	Maize	Elevated maximum daily temperature induces alternative splicing and the roles of SR (serine/arginine-rich) 45a	[70]
HSF2A, HSFs	Arabidopsis, maize	HSF2A alternative splicing in response to heat stress	[30,71,72]
SR genes	Arabidopsis	Alternative splicing of SR genes in response to abiotic stress, including heat stress	[73]
FLM	Arabidopsis	Heat-induced alternative splicing of FLM (FLOWERING LOCUS M) isoforms and temperature dependent flowering	[74,75,76,77,78]
miR156-SPL	Arabidopsis	The miR156-SPL module mediates the response to recurring heat stress in Arabidopsis	[79]
miRNAs	Arabidopsis, maize	Identification of the miRNA in Arabidopsis and maize involved in post-transcriptional regulation of the response to heat stress	[80,81]