Arabidopsis thaliana Ubiquitin-Associated Protein 1 (AtUAP1) Interacts with Arabidopsis thaliana Ring Zinc Finger 1 (AtRZF1) to Negatively Regulate Dehydration Response.

Ubiquitination, one of the most frequently occurring post-translational modifications, is essential for regulating diverse cellular processes in plants during abiotic stress. The E3 ubiquitin (Ub) ligase AtRZF1 mutation is known to enhance drought tolerance in Arabidopsis thaliana seedlings. To further investigate the function of AtRZF1 in osmotic stress, we isolated AtUAP1 which interacts with AtRZF1 using a yeast two-hybrid system. AtUAP1, a ubiquitin-associated motif containing protein, increased the amount of Ub-conjugated AtRZF1. Moreover, AtUAP1 RNAi lines were more tolerant to osmotic stress than wild-type, whereas AtUAP1-overexpressing transgenic lines showed sensitive responses, including cotyledon greening, water loss, proline accumulation, and changes in stress-related genes expression, indicating that AtUAP1 could negatively regulate dehydration-mediated signaling. In addition, AtUAP1-Green Fluorescent Protein fusion protein (AtUAP1-GFP) was observed in the nuclei of root cells of transgenic seedlings. Genetic studies showed that the AtRZF1 mutation could rescue the sensitive phenotype of AtUAP1-overexpressing lines in response to osmotic stress, suggesting that AtRZF1 was epistatic to AtUAP1 in dehydration signaling. Taken together, our findings describe a new component in the AtRZF1 ubiquitination pathway which controls the dehydration response in A. thaliana.