Membrane-mediated salt stress signaling in flowering time control.

More than 10% of the plant-specific NAC (NAM, ATAF1/2, CUC2) transcription factors have been predicted to have alpha-helical transmembrane (TM) domain in their C-terminal regions, among which at least three members have been proven to be membrane-associated and play a role in cell cycle control and stress responses. These observations suggest that membrane-mediated regulation would be an important molecular mechanism mediating rapid transcriptional responses to internal and external stimuli in plants. Recently, we showed that a salt-responsive NTL (NTM1-Like's) transcription factor NTL8 is localized primarily in plasma membranes as dormant form and subsequently processed into transcriptionally active, nuclear form. Overexpression of an active NTL8 form exhibited delayed flowering as well as reduced growth with small curled leaves. Consistent with this, expression of FLOWERING LOCUS T (FT) and its downstream genes was significantly reduced in the transgenic plants. Furthermore, FT was notably repressed by high salt. These results indicate that NTL8 mediates salt-responsive flowering via FT in Arabidopsis and that membrane-mediated transcription regulation underlies the salt signaling in mediating flowering initiation.

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