| Category | Key findings | Evidence type/assay | Primary reference |
|---|---|---|---|
| Identity/domains | HSFA3 = Arabidopsis thaliana At5g03720 (HSF17), a class A heat-shock transcription factor. Plant class A HSFs contain a conserved DNA-binding domain (DBD), HR-A/B oligomerization region, NLS/NES motifs, and a C-terminal activator domain; class A activity is associated with AHA-like activation motifs, although HsfA3 has an atypical activator region in which canonical AHA motifs are replaced by Trp-rich features. HSFs bind HSEs in promoters. (pqac-00000011, pqac-00000016, pqac-00000018) | Review synthesis of HSF structure/function; family/domain analysis | Guo et al. 2016, Front. Plant Sci., https://doi.org/10.3389/fpls.2016.00114; Fragkostefanakis et al. 2015, Plant Cell Environ., https://doi.org/10.1111/pce.12396 |
| Upstream regulators | DREB2A acts upstream of HSFA3 in heat stress. DREB2A and DREB2B strongly activated a PHsfA3:GUS reporter by up to ~20-fold; dreb2a knockout backgrounds show delayed/reduced HSFA3 induction. A constitutively active DREB2A system also upregulates HSFA3. HSFA3 expression is additionally integrated with HSFA1-class signaling; loss of HSFA1d/HSFA1e lowers HSFA3 induction under heat/excess light. NF-YA2/NF-YB3/DPB3-1 synergize with DREB2A on the HSFA3 promoter through a CCAAT box. (pqac-00000005, pqac-00000008, pqac-00000009, pqac-00000010, pqac-00000000) | Promoter::GUS transactivation in protoplasts; mutant expression analysis; cooperative transactivation assays | Schramm et al. 2008, Plant J., https://doi.org/10.1111/j.1365-313x.2007.03334.x; Sato et al. 2014, Plant Cell, https://doi.org/10.1105/tpc.114.132928 |
| Promoter cis-elements | HSFA3 promoter contains functionally important DRE/CRT motifs. Mutation of DRE1 caused a dramatic drop in reporter activity; combined DRE1 + DRE2 mutation abolished activity. One mapped high-affinity site (DRE1) has sequence **AACCGACAA** with the DRE core **CCGAC**. In the 1-kb promoter, mutation of **CCAAT4** abolished the extra synergistic activation by NF-YA2/NF-YB3/DPB3-1 plus DREB2A-CA. (pqac-00000003, pqac-00000004, pqac-00000005, pqac-00000009) | Site-directed promoter mutagenesis; EMSA; protoplast GUS assays | Schramm et al. 2008, Plant J., https://doi.org/10.1111/j.1365-313x.2007.03334.x; Sato et al. 2014, Plant Cell, https://doi.org/10.1105/tpc.114.132928 |
| Direct DNA binding/targets | Recombinant HsfA3 binds HSE-containing promoter regions of small heat-shock protein genes, including **Hsp18.1-CI** and **Hsp26.5-MII**; HsfA3 strongly activates these promoters, whereas DREB2A alone does not directly activate Hsp18.1-CI without HSFA3. HsfA3 DNA-binding mutants (reported as **R109A / R98A** in the DBD context) abolish binding. Additional downstream genes cited in review context include **HSP70**. (pqac-00000003, pqac-00000004, pqac-00000007, pqac-00000010) | EMSA with GST fusion proteins; transient reporter assays; mutational analysis | Schramm et al. 2008, Plant J., https://doi.org/10.1111/j.1365-313x.2007.03334.x |
| Localization | As an HSF, HSFA3 is inferred to function in the nucleus because plant class A HSFs carry NLS/NES motifs and activate transcription via promoter binding. The retrieved context did not contain a direct AtHSFA3 subcellular localization experiment; thus nuclear localization is best treated as strong family-based inference rather than direct HSFA3-specific visualization evidence. (pqac-00000011, pqac-00000016) | Domain/family inference from authoritative reviews | Guo et al. 2016, Front. Plant Sci., https://doi.org/10.3389/fpls.2016.00114 |
| Phenotypes | Loss-of-function hsfA3 lines (T-DNA + RNAi) show reduced thermotolerance: **30–40% lower germination after heat**, hypocotyl elongation reduced to **40–50% of WT**, and seedling survival reduced by about **60%**. These lines also show reduced accumulation/expression of **Hsp101** and small HSPs under heat. Overexpression of AtHSFA3 elevates thermotolerance, but reviews note accompanying growth penalties/dwarfism in some overexpression backgrounds. (pqac-00000003, pqac-00000007, pqac-00000001, pqac-00000014) | T-DNA/RNAi mutant thermotolerance assays; hypocotyl elongation, germination, survival assays; immunoblotting | Schramm et al. 2008, Plant J., https://doi.org/10.1111/j.1365-313x.2007.03334.x; Jacob et al. 2017, Plant Biotechnol. J., https://doi.org/10.1111/pbi.12659 |
| Role in heat-stress memory | Recent reviews place HSFA3 among core thermomemory regulators. HSFA2–HSFA3 complexes are reported to bind promoters of memory genes and promote **H3K4 methylation/H3K4me3**, linking HSFA3 to sustained transcription after priming. HSFA3 is also discussed together with memory modules involving **HSP101**, **HSA32**, **HSP21**, **APX2**, and **HSP22**, although the most explicit complex-level evidence in the retrieved context concerns HSFA2–HSFA3 and chromatin-based memory. (pqac-00000019, pqac-00000020, pqac-00000021) | Recent review synthesis of genetic/chromatin studies on thermomemory | Zheng et al. 2024, Int. J. Mol. Sci., https://doi.org/10.3390/ijms25168976; Bakery et al. 2024, New Phytol., https://doi.org/10.1111/nph.20017 |
| Quantitative expression data | In Arabidopsis RNA-seq heat-stress data, AtHSFA3 expression increased from **FPKM 0.58** (WT, no stress) to **10.50** (WT, heat), corresponding to **log2FC 4.17**; in a 35S-AtHSFA1b background under heat it was **FPKM 1.70**, **log2FC 1.54**. These values support strong heat inducibility and context-dependent regulation within the HSF network. (pqac-00000002) | RNA-seq / transcript quantification | Albhilal 2015 thesis dataset summary citing Arabidopsis HSFA1b network analysis |
| Network position | HSFA3 appears to participate in a hierarchical relay: DREB2A → HSFA3 → HSP genes, while HSFA3 overexpression can also upregulate other HSFs such as **HSFA1e, HSFA7b, HSFB2a/HSFB2b**, indicating feedback/feed-forward amplification within the heat-shock transcriptional network. (pqac-00000000, pqac-00000014) | Expression/network analysis; overexpression studies summarized in reviews | Jacob et al. 2017, Plant Biotechnol. J., https://doi.org/10.1111/pbi.12659 |


*Table: This table condenses experimentally supported and review-backed findings for Arabidopsis HSFA3/At5g03720, including identity, regulatory inputs, promoter motifs, targets, phenotypes, thermomemory role, and quantitative expression data. It is designed as a quick-reference artifact for functional annotation with context-ID citations.*