A Novel Plant U-Box Ubiquitin Ligase Regulated by Abiotic Stress and Hormone

Proteostasis maintenance under stress and the non-stress condition is key for plant function, growth, and development. The stress response is also characterized by global changes in cellular proteostasis achieved by a balance between protein synthesis and degradation. The Ubiquitin Proteasome System (UPS) is a vital player in regulating proteostasis. Proteins destined to be degraded by the 26S proteasome are tagged with short ubiquitin chains via a 3-step pathway. The last step, conferring target specificity, is catalyzed by E3 ubiquitin ligases. The Arabidopsis genome encodes ca 1,400 E3 genes, which play essential roles in plant development, biotic-abiotic stress, and phytohormone signaling. Here we present a study on an Arabidopsis ubiquitin ligase, belonging to the Plant U-Box (PUB) sub-family, with a role in abiotic stress and development. The T-DNA insertion mutants are drought hypersensitive. This PUB is also involved in the development of lateral roots, a process modulated by the plant hormone auxin, with the T-DNA mutants showing reduced lateral root density compared with wild-type plants. Furthermore, promoter activity is regulated by treatment with agents that cause abiotic stress and by auxin. Auxin modulates both the protein levels and the subcellular localization of this PUB E3. Thus, this ubiquitin ligase may act in the cross-talk between abiotic stress and development.