Abstract
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.
Highlights
Plant hormone gibberellins (GA) have been hypothesized to play important roles in regulating various developmental processes in plants, such as stem elongation, leaf expansion, seed germination and flower development[1]
GIBBERELLIN SUPPRESSING FACTOR (GSF) acts as a transcriptional activator based on the activation assay in yeast
The nature of GSF as a transcriptional activator was further supported by the result that a similar altered dwarfism phenotype was observed in 35S-Ω promoter (35S)::GSF-transmembrane domain (TM) and 35S::GSF-TM + VP16 transgenic Arabidopsis
Summary
Plant hormone gibberellins (GA) have been hypothesized to play important roles in regulating various developmental processes in plants, such as stem elongation, leaf expansion, seed germination and flower development[1]. In Arabidopsis, the gibberellin biosynthetic genes encode such enzymes as ent-copalyl diphosphate synthase (CPS), ent-kaurene synthase (KS) and ent-kaurene oxidase (KO), which catalyze the early steps of GA biosynthesis. To maintain the dynamic homeostasis of gibberellin for plant growth, the deactivation of GA by GA2oxs is important for the regulation of the concentration of bioactive gibberellin in plants[1,6]. It has been reported that GA could play a vital role in response to abiotic stresses in plants[7]. Additional evidence was reported that indicates that GA could respond to abiotic stresses by modulating plant growth via GA biosynthesis or signal transduction[7]. The GA2oxs were upregulated to induce the GA deactivation in response to salt and cold stresses in Arabidopsis[9,10,11]. The manner in which the mechanisms control GA levels during abiotic stresses still remained to be investigated
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