Abstract
HEAT SHOCK FACTOR A2 (HSFA2) is a regulator of multiple environmental stress responses required for stress acclimation. We analyzed HSFA2 co-regulated genes and identified 43 genes strongly co-regulated with HSFA2 during multiple stresses. Motif enrichment analysis revealed an over-representation of the site II element (SIIE) in the promoters of these genes. In a yeast 1-hybrid screen with the SIIE, we identified the closely related R2R3-MYB transcription factors TT2 and MYB5. We found overexpression of MYB5 or TT2 rendered plants heat stress tolerant. In contrast, tt2, myb5, and tt2/myb5 loss of function mutants showed heat stress hypersensitivity. Transient expression assays confirmed that MYB5 and TT2 can regulate the HSFA2 promoter together with the other members of the MBW complex, TT8 and TRANSPARENT TESTA GLABRA 1 (TTG1) and that the SIIE was involved in this regulation. Transcriptomic analysis revealed that TT2/MYB5 target promoters were enriched in SIIE. Overall, we report a new function of TT2 and MYB5 in stress resistance and a role in SIIE-mediated HSFA2 regulation.
Highlights
Heat shock factors (HSFs) represent a widely conserved class of transcription factors involved in stress response and development [1,2]
We showed that TESTA 2 (TT2)/MYB5-mediated HFSA2 expression is significantly enhanced in the presence of TESTA 8 (TT8) and TESTA GLABRA 1 (TTG1), two other members of the MBW complex
Promoters of HEAT SHOCK FACTOR A2 (HSFA2) Coregulated Genes Are Enriched in the Site II Element Motif
Summary
Heat shock factors (HSFs) represent a widely conserved class of transcription factors involved in stress response and development [1,2]. The function of TT2 in PA accumulation requires its interaction with a bHLH (TT8) and a WDR protein (TRANSPARENT TESTA GLABRA1 [TTG1]) to form an MBW (MYB/bHLH/WDR) complex that regulates several late anthocyanin/PA biosynthetic genes (LBGs). We showed that TT2/MYB5-mediated HFSA2 expression is significantly enhanced in the presence of TT8 and TTG1, two other members of the MBW complex Consistent with this result, Arabidopsis plants overexpressing TT2 and, to a lesser extent MYB5, exhibit enhanced resistance to heat stress and tt, myb, tt8 and tt2/myb loss of function mutants are more sensitive to heat stress. Promoter enrichment analysis of differentially regulated gene networks revealed two different modes of transcriptional regulation, one depending on the AC-rich element and the E-box (secondary metabolic process related genes), and the other involving the SIIE, the E-box, and the HSE (genes involved in stress response). We report a new function of TT2 and MYB5 in stress response
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