The Seed Development Factors TT2 and MYB5 Regulate Heat Stress Response in Arabidopsis

Abstract

<i>HEAT SHOCK FACTOR A2</i> (<i>HSFA2</i>) is a regulator of multiple environmental stress responses required for stress acclimation. We analyzed <i>HSFA2</i> co-regulated genes and identified 43 genes strongly co-regulated with <i>HSFA2</i> 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 <i>MYB5</i> or <i>TT2</i> rendered plants heat stress tolerant. In contrast, <i>tt2</i>, <i>myb5</i>, and <i>tt2/myb5</i> loss of function mutants showed heat stress hypersensitivity. Transient expression assays confirmed that MYB5 and TT2 can regulate the <i>HSFA2</i> 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 <i>TT2/MYB5</i> 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 <i>HSFA2</i> regulation.