Ethylene Regulates Arabidopsis Development via the Modulation of DELLA Protein Growth Repressor Function

Abstract

Phytohormones regulate plant development via a poorly understood signal response network. Here, we show that the phytohormone ethylene regulates plant development at least in part via alteration of the properties of DELLA protein nuclear growth repressors, a family of proteins first identified as gibberellin (GA) signaling components. This conclusion is based on the following experimental observations. First, ethylene inhibited Arabidopsis root growth in a DELLA-dependent manner. Second, ethylene delayed the GA-induced disappearance of the DELLA protein repressor of ga1-3 from root cell nuclei via a constitutive triple response-dependent signaling pathway. Third, the ethylene-promoted "apical hook" structure of etiolated seedling hypocotyls was dependent on the relief of DELLA-mediated growth restraint. Ethylene, auxin, and GA responses now can be attributed to effects on DELLA function, suggesting that DELLA plays a key integrative role in the phytohormone signal response network.

DELLAs Contribute to Plant Photomorphogenesis

“…It has recently become apparent that DELLAs integrate endogenous and environmental cues in the regulation of plant growth (Achard et al, 2003(Achard et al, , 2006Fu and Harberd, 2003;Alvey and Harberd, 2005). DELLAs are nuclear growth repressors and GA relieves DELLA restraint by promoting the destruction of DELLAs in the proteasome (Silverstone et al, 2001;Dill et al, 2004;Fu et al, 2004).…”

“…pRGA:GFP-RGA seedlings express a GFP-RGA fusion protein that is detectable in root cell nuclei and destroyed rapidly in response to GA treatment (Silverstone et al, 2001;Achard et al, 2003). Because light inhibits hypocotyl growth via a DELLA-dependent mechanism, we determined the effect of light on GFP-RGA in nuclei of elongating cells of the hypocotyl.…”

“…pRGA:GFP-RGA-containing lines were grown on GM plates for 2 d in darkness and subsequently either maintained in the dark or transferred to white light for 5 d. Seedlings were then exposed to dark or light for the time as indicated before observation of hypocotyls by confocal microscopy (Achard et al, 2003).…”

“…All seeds were surface sterilized and placed on germination medium (GM) plates (Achard et al, 2003) at 4°C for 4 d to synchronize germination. For experiments involving ga1-3, all lines were GA treated (10 mM GA 3 ) for 3 d at 4°C, then washed three times with distilled water before sterilization.…”

Epidermal Cell Death in Rice Is Regulated by Ethylene, Gibberellin, and Abscisic Acid

“…GA promotes root growth in Arabidopsis through proteasome-mediated degradation of the DELLA proteins RGA (repressor of gal-3) and GAI (gibberellic acid insensitive), which act as root growth repressors (Fu et al, 2002;Fu and Harberd, 2003;Fleet and Sun, 2005). Ethylene delays GA-promoted degradation of RGA in Arabidopsis roots and thus maintains root growth inhibition (Achard et al, 2003). Thus, DELLA proteins appear to be one point at which ethylene and GA signaling pathways meet.…”