The Ubiquitin-Binding Protein OsDSK2a Mediates Seedling Growth and Salt Responses by Regulating Gibberellin Metabolism in Rice

UBL-UBA (ubiquitin-like-ubiquitin-associated) proteins are ubiquitin receptors and transporters in the ubiquitin-proteasome system that play key roles in plant growth and development. High salinity restricts plant growth by disrupting cellular metabolism, but whether UBL-UBA proteins are involved in this process is unclear. Here, we demonstrate that the novel UBL-UBA protein OsDSK2a (DOMINANT SUPPRESSOR of KAR2) mediates seedling growth and salt responses in rice (Oryza sativa). Through analysis of osdsk2a, a mutant with retarded seedling growth, as well as in vitro and in vivo assays, we demonstrated that OsDSK2a combines with polyubiquitin chains and interacts with the gibberellin (GA)-deactivating enzyme ELONGATED UPPERMOST INTERNODE (EUI), resulting in its degradation through the ubiquitin-proteasome system. Bioactive GA levels were reduced and plant growth was retarded in the osdsk2a mutant. By contrast, eui mutants displayed increased seedling growth and bioactive GA levels. OsDSK2a levels decreased in plant under salt stress. Moreover, EUI accumulated under salt stress more rapidly in osdsk2a than in wild-type plants. Thus, OsDSK2a and EUI play opposite roles in regulating plant growth under salt stress by affecting GA metabolism. Downregulation of the ubiquitin-binding receptor OsDSK2a increases EUI accumulation, which promotes GA metabolism and reduces plant growth under salt stress.