The ubiquitination pathway has been found to regulate plant responses to environmental stress. However, the role of E3 ubiquitin ligase in desiccation tolerant moss has not yet been elucidated. Previous research has shown that the abscisic acid (ABA) signaling factor ScABI3 can significantly increase desiccation tolerance and reduce ABA sensitivity in the desert moss Syntrichia caninervis. In this study, we identified a RING-type E3 ubiquitin ligase, ScPRT1, and showed that ScABI3 can directly interact with ScPRT1 in vitro and in vivo. Furthermore, we found that the high expression of ScPRT1 can interfere with the transcription of ScABI3 under ABA treatment. Therefore, we speculate that ScPRT1 may degrade ScABI3 through the ubiquitin-26S proteasome system and participate in ABA-dependent signaling in response to ABA-insensitivity or desiccation tolerance in S. caninervis. The findings from our study may enrich our knowledge of the role of E3 ubiquitin ligase in desiccation tolerance and lay a theoretical foundation for an in-depth study of the relationship between ubiquitination modification and ABA signal transduction under environmental stress.

ABI3 (ABSCISIC ACID INSENSITIVE 3) is a family of B3 transcription factors essential for regulating the abscisic acid (ABA) signaling pathway involved in various biological processes and abiotic stress. Our previous studies demonstrated that ectopic expression of ScABI3 from a desiccation-tolerant moss (Syntrichia caninervis) into Arabidopsis thaliana enhanced abiotic stress tolerance. However, studies on plant transformation using the ABI3 gene are limited and other possible functions of ScABI3 are not known. Here, we transformed the ScABI3 into alfalfa (Medicago sativa L.) and analyzed the effects on phenotype, photosynthetic efficiency, and nutritional quality. The results showed that the endogenous ABA content of the transgenic plants was significantly higher than WT, and the leaf-stem ratio, leaf area, and branch number increased with ScABI3 overexpression in alfalfa. Further analysis of the gas exchange parameters showed that the net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and water-use efficiency (WUE) of the transgenic alfalfa were significantly higher than WT; meanwhile, the protein content of the transgenic lines was higher than the WT, but the crude fat content was lower. Thus, these findings suggest that ScABI3 can be used as a potential candidate gene to manipulate alfalfa’s growth and nutritional quality. This study will provide a theoretical basis for breeding alfalfa varieties and assist in forage production and animal husbandry in the future.