An F-box E3 ubiquitin ligase-coding gene AtDIF1 is involved in Arabidopsis salt and drought stress responses in an abscisic acid-dependent manner

- DROUGHT INDUCED F-BOX 1 (DIF1) is a member of the F-box superfamily.
- AtDIF1 can regulate an adaptive response of Arabidopsis to salt and drought stress.
- AtDIF1 overexpression promoted seedling growth and reducing Na+ content.
- AtDIF1 overexpression enhanced seed germination and seedling growth with ABA.
- AtDIF1 plays roles in a positive response to salt, but a negative response to drought stress.

F-box protein is a subunit of E3 ubiquitin ligase for protein degradation through an ubiquitination pathway and plays multiple roles in plant development and stress responses. DROUGHT INDUCED F-BOX 1 (DIF1) is a member of the F-box superfamily. Whether it is involved in abiotic stress responses remains unknown. Here we show a role of AtDIF1 in regulating an adaptive response of Arabidopsis to salt and drought stresses. Expression of AtDIF1 was induced by salinity, drought and abscisic acid (ABA), but repressed by cold treatment. Analysis of AtDIF1 transcripts revealed its expression in various tissues and organs of Arabidopsis. AtDIF1 was mainly located in the nucleus and to lesser extent in cytoplasm. AtDIF1 overexpression conferred plant tolerance to salt stress by promoting seedling growth and reducing the content of Na+ and loss of K+. These observations could be genetically confirmed by the adverse phenotypes of a knockout mutant dif1. Transgenic plants overexpressing AtDIF1 showed less tolerance to drought stress, with regard to the reduced seed germination and post-germination growth of seedlings and less survival rate after a prolonged dehydration treatment, whereas the dif1 mutants were more tolerant to the drought stress. Furthermore, the AtDIF1 transgenic plants in the presence of ABA displayed enhanced seed germination and seedling growth, while the dif1 mutant plants showed a contrasting phenotype. Expression of ABA-synthetic and stress-responsive marker genes such as ABI1, ABI2, ABI5, ABF3, PP2CA, and RD29A was up-regulated in dif1 mutant plants but down-regulated in 35S::DIF1 plants. These results suggest that AtDIF1 is able to play a role in a positive response to salt, but a negative response to drought stress in an ABA-dependent manner.