Jiajin Xu

Ubiquitin-specific proteases (UBPs), the largest subfamily of deubiquitinating enzymes (DUBs), are critical for plant growth and development as well as abiotic-stress responses. In this study, we discovered that the expression of the ubiquitin-specific protease 15 (UBP15) gene was induced by salt, mannitol and abscisic acid (ABA) treatments. Further research revealed that UBP15 is involved in modulation of salt, drought tolerance and ABA signaling during seed germination, early seedling development, post-germination root growth or adult-plant stage. Enrichment analysis showed that many genes related to abiotic stresses and metabolic pathways were altered in the ubp15-1 mutant. Through the joint analysis of the quantitative real-time polymerase chain reaction (qRT-PCR) and differentially-expressed gene relationship network, we found that UBP15 may mainly regulate salt-stress tolerance by modulating the dwarf and delayed flowering 1 (DDF1) pathway through a cascade reaction. In the regulation of drought-stress responses, ring domain ligase1 (RGLG1) may be a direct substrate of UBP15. Moreover, we cannot exclude the possibility that UBP15 acts in a feed-forward loop mechanism in the regulation of drought-stress responses via ethylene response factor 53 (ERF53) and its ubiquitin (Ub) ligase RGLG1. In ABA signal transduction, UBP15 may play a role in at least three aspects of the ABA signaling pathway: ABA synthesis, stomatal closure regulated by ABA signaling, and transcription factors in the ABA pathway. Taken together, our results suggest that UBP15 is involved in salt, osmotic, and drought-stress tolerance and the ABA signaling pathway by directly regulating the stability of key substrates or indirectly affecting the expression of genes related to abiotic stresses in Arabidopsis thaliana. Our research provides new germplasm resources for stress-resistant crops cultivation. These results demonstrate that UBP15 is a key regulator of salt, drought and ABA tolerance in Arabidopsis.

The ubiquitin-specific protease (UBP) family represents a type of deubiquitinase (DUB) that plays a significant role in plant abiotic stress responses, growth, and development. Although UBP genes have been characterized in many species, a genome-wide systematic analysis and the potential functions under abiotic stresses have not yet been reported in rice (Oryza sativa L.). In this study, we identified 21 UBP gene family members in the genome of rice, all of which had UCH domains containing short but highly conserved Cys-box and His-box. The DUF4220 and DUF594 domains, which are found in monocotyledonous plants, were unique. Phylogenetic analysis suggested that OsUBP7 and OsUBP12 genes had the closest genetic relationships with AtUBP12 and AtUBP13, implying that OsUBP7 and OsUBP12 might have similar biological functions to AtUBP12 and AtUBP13. Synteny analysis revealed that OsUBP genes were expanded through segmental duplication under purifying selection. Meanwhile, they had closer evolutionary relationships with monocotyledonous plants. Additionally, all OsUBP genes had an ABRE cis-element, which was related to abscisic acid (ABA) stress hormone response. Protein interaction analysis suggested that OsUBP22 might modulate gene regulation through OsGCN5- and OsADA2-mediated chromatin modification, and OsUBP10 might regulate salt stress through modulating OsDNA2_4 stability. Specifically, the expression profiles and the transcriptional levels of 11 representative OsUBPs suggested the potential important functions of OsUBP9 and OsUBP17 under drought and cold stresses. Taken together, our study provided a systematic analysis of OsUBPs and preliminarily explored their potential roles under abiotic stresses. Our results lay a foundation for further research on the functions of the OsUBP gene family under abiotic stresses.