DELLAs Function as Coactivators of GAI-ASSOCIATED FACTOR1 in Regulation of Gibberellin Homeostasis and Signaling inArabidopsis   

Abstract

Gibberellins (GAs) are essential regulators of plant development, and DELLAs are negative regulators of GA signaling. The mechanism of GA-dependent transcription has been explained by DELLA-mediated titration of transcriptional activators and their release through the degradation of DELLAs in response to GA. However, the effect of GA on genome-wide expression is predominantly repression, suggesting the existence of unknown mechanisms of GA function. In this study, we identified an Arabidopsis thaliana DELLA binding transcription factor, GAI-ASSOCIATED FACTOR1 (GAF1). GAF1 shows high homology to INDETERMINATE DOMAIN1 (IDD1)/ENHYDROUS. GA responsiveness was decreased in the double mutant gaf1 idd1, whereas it was enhanced in a GAF1 overexpressor. GAF1 binds to genes that are subject to GA feedback regulation. Furthermore, we found that GAF1 interacts with the corepressor TOPLESS RELATED (TPR) and that DELLAs and TPR act as coactivators and a corepressor of GAF1, respectively. GA converts the GAF1 complex from transcriptional activator to repressor via the degradation of DELLAs. These results indicate that DELLAs turn on or off two sets of GA-regulated genes via dual functions, namely titration and coactivation, providing a mechanism for the integrative regulation of plant growth and GA homeostasis.

Epigenetic Modifications and Plant Hormone Action

“…For example, the EAR motif was identified in several proteins, including NOVEL INTERACTOR OF JAZ (NINJA), ABI-FIVE BINDING PROTEINS (AFPs), BRASSINAZOLE RESISTANT1 (BZR1) and BRI1-EMS-SUPPRESSOR 1 (BES1), and are involved in ethylene, JA, ABA, gibberellic acid (GA) and brassinosteroid (BR) signaling (Pauwels et al, 2010; Oh et al, 2014; Fukazawa et al, 2014; Ryu et al, 2014). In particular, the EAR repressome and the signaling pathways leading to the degradation of the EAR repressors are essentially paralleled in auxin and JA signaling (Pérez and Goossens., 2013).…”

“…In particular, the EAR repressome and the signaling pathways leading to the degradation of the EAR repressors are essentially paralleled in auxin and JA signaling (Pérez and Goossens., 2013). TPL and its family proteins TOPLESS-RELATED (TPRs) are implicated in auxin, JA, GA and BR signaling (Pauwels et al, 2010; Oh et al, 2014; Fukazawa et al, 2014; Ryu et al, 2014). The same mechanisms involving HDACs via TPL may be employed by other plant hormone regulatory machineries.…”

“…Solid lines indicate direct interaction and dotted lines indicate functional association or regulation. Ninja protein (Pauwels et al, 2010), GAF1 (Fukazawa et al, 2014), IAA proteins (Fukaki et al, 2006; Long et al, 2006), BES1 (Ryu et al, 2014), BZR1 (Oh et al, 2014) and DELLA proteins (Zhang et al, 2104). (B) A hypothetical auxin-linked epigenetic regulation loop.…”

Long-term monitoring of bioluminescence circadian rhythms of cells in a transgenic <i>Arabidopsis</i> mesophyll protoplast culture

“…The MSP medium contains 1×MS salts, 1% sucrose, 400 mM mannitol, 2 mg/L glycine, 100 mg/L myo-inositol, 3 mg/L thiamin hydrochloride, 5 mg/L nicotinic acid, 0.5 mg/L pyridoxine hydrochloride, KOH (pH 5.6). Phytohormones [1 µM NAA (1-Naphthaleneacetic Acid), 0.2 µM kinetin] were added to the MSP medium to make the MSP+PH medium (Fukazawa et al 2014;Satoh et al 2004). …”

Plant development regulation: Overview and perspectives

“…GA biosynthesis is linked to the transport of auxin by PIN1 . Other DELLAs such as GA-INSENSITIVE (GAI), REPRESSOR of GA1-3 (RGA), or GAI-ASSOCIATED FACTOR1 (GAF1) regulates GAs signalling and GAs homeostasis in Arabidopsis (Peng et al, 1997;Fukazawa et al, 2014) and rice (Fu et al, 2001). …”