NAC-Like Gene GIBBERELLIN SUPPRESSING FACTOR Regulates the Gibberellin Metabolic Pathway in Response to Cold and Drought Stresses in Arabidopsis.

To investigate the functions of NAC-like genes, we reported the characterization and functional analysis of one Arabidopsis NAC-like gene which showed a novel function in the regulation of gibberellin biosynthesis and named as GIBBERELLIN SUPPRESSING FACTOR (GSF). GSF acts as a transcriptional activator and has transactivation capacity based on yeast transcription activity assays. YFP + GSF-TM (lacking a transmembrane domain) fusion proteins accumulated in the nuclei, while the YFP + GSF fusion proteins only accumulated in the ER membrane and were absent from the nuclei. These results revealed that GSF requires processing and release from the ER and transportation into the nucleus to perform its function. The ectopic expression of GSF-TM caused a dwarfism phenotype, which was correlated with the upregulation of the gibberellin (GA) deactivation genes GA2-oxidases 2/6 (GA2ox2/6) and the downregulation of the GA biosynthetic genes GA20-oxidases 1-4 (GA20ox1-4). The external application of GA rescued the dwarfism in the 35 S::GSF-TM plants, indicating that GSF affects GA biosynthesis, rather than the GA signaling pathway. Further analysis indicated that the upregulation of GA2ox2/6 is a key factor for the GSF function to regulate the GA level, since 35 S::GA20ox1 could not rescue the dwarfism in the 35 S::GSF-TM plants. Cold treatment induced the processing of the YFP + GSF fusion proteins from the ER membrane and their entry into the nuclei, which is correlated with the cold-induced upregulation of GA2oxs. In addition, the expression of GA2oxs was induced by drought, and the 35 S::GSF-TM plants showed drought tolerance compared to the wild-type plants. Our data suggest a role for GSF in response to abiotic stresses, such as cold and drought, by suppressing the biosynthesis of GA in Arabidopsis.

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