PT - JOURNAL ARTICLE AU - Fu, Xiangdong AU - Richards, Donald E. AU - Ait-ali, Tahar AU - Hynes, Llewelyn W. AU - Ougham, Helen AU - Peng, Jinrong AU - Harberd, Nicholas P. TI - Gibberellin-Mediated Proteasome-Dependent Degradation of the Barley DELLA Protein SLN1 Repressor AID - 10.1105/tpc.006197 DP - 2002 Dec 01 TA - The Plant Cell PG - 3191--3200 VI - 14 IP - 12 4099 - http://www.plantcell.org/content/14/12/3191.short 4100 - http://www.plantcell.org/content/14/12/3191.full SO - Plant Cell2002 Dec 01; 14 AB - DELLA proteins are nuclear repressors of plant gibberellin (GA) responses. Here, we investigate the properties of SLN1, a DELLA protein from barley that is destabilized by GA treatment. Using specific inhibitors of proteasome function, we show that proteasome-mediated protein degradation is necessary for GA-mediated destabilization of SLN1. We also show that GA responses, such as the aleurone α-amylase response and seedling leaf extension growth, require proteasome-dependent GA-mediated SLN1 destabilization. In further experiments with protein kinase and protein phosphatase inhibitors, we identify two additional signaling steps that are necessary for GA response and for GA-mediated destabilization of SLN1. Thus, GA signaling involves protein phosphorylation and dephosphorylation steps and promotes the derepression of GA responses via proteasome-dependent destabilization of DELLA repressors.