Repression by an auxin/indole acetic acid protein connects auxin signaling with heat shock factor-mediated seed longevity

• Published in: Proceedings of the National Academy of Sciences - PNAS 2010-12, Vol.107 (50), p.21908-21913
• Main Authors: Carranco, Raúl, Espinosa, José Manuel, Prieto-Dapena, Pilar, Almoguera, Concepción, Jordano, Juan, Estelle, Mark
• Format: Article
• Language: English
• Subjects: Auxins; Biological Sciences; Embryos; Flowers & plants; Fluorescence; Gene expression; Heat shock proteins; Heat-Shock Proteins - genetics; Heat-Shock Proteins - metabolism; Helianthus - embryology; Helianthus - metabolism; Helianthus - physiology; Hormones; Immatures; Indoleacetic Acids - metabolism; Molecular Sequence Data; Nicotiana - genetics; Nicotiana - metabolism; Plant cells; Plant Growth Regulators - genetics; Plant Growth Regulators - metabolism; Plant Proteins - genetics; Plant Proteins - metabolism; Plants; Plants, Genetically Modified - genetics; Plants, Genetically Modified - metabolism; Plasmids; Proteins; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; Repression; Seeds - physiology; Signal transduction; Signal Transduction - physiology; Sunflowers; Transcription Factors - genetics; Transcription Factors - metabolism; Two-Hybrid System Techniques; Yeasts
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1014856107

The plant hormone auxin regulates growth and development by modulating the stability of auxin/indole acetic acid (Aux/IAA) proteins, which in turn repress auxin response factors (ARFs) transcriptional regulators. In transient assays performed in immature sunflower embryos, we observed that the Aux/IAA protein HaIAA27 represses transcriptional activation by HaHSFA9, a heat shock transcription factor (HSF). We also found that HaIAA27 is stabilized in immature sunflower embryos, where we could show bimolecular fluorescence complementation interaction between native forms of HaIAA27 and HaHSFA9. An auxin-resistant form of HaIAA27 was overexpressed in transgenic tobacco seeds, leading to effects consistent with down-regulation of the ortholog HSFA9 gene, effects not seen with the native HaIAA27 form. Repression of HSFs by HaIAA27 is thus likely alleviated by auxin in maturing seeds. We show that HSFs such as HaHSFA9 are targets of Aux/IAA protein repression. Because HaHSFA9 controls a genetic program involved in seed longevity and embryonic desiccation tolerance, our findings would suggest a mechanism by which these processes can be auxin regulated. Aux/IAA-mediated repression involves transcription factors distinct from ARFs. This finding widens interpretation of auxin responses.