Regulation of flowering time in Arabidopsis



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Flowering pathway

Gibberellin pathway



The Gibberellin transduction pathway




DDF1 gene and protein:

DDF1 encodes a putative protein of 209 amino-acids that shows sequence similarities with dehydration-responsive element binding protein (DREB1)/C-repeat binding factor genes (CBF), shown to be generally involved in stress responses (Magome et al., 2004).

The predicted protein contains AP2 transcription factor motifs, a Serine-rich domain in the C-terminus, and a putative nuclear localization signal in the N-terminus (Magome et al., 2004).

The DDF1 sequence shares 69% sequence identity with DDF2. Both ddf1 and ddf2 mutants have a similar phenotype and respond similarly to exogenous GA treatment (Magome et al., 2004).

DDF1 expression:

DDF1 is expressed in all the tissues that have been analyzed. Its expression is very high in the stem and the rosette leaves, still high in the cauline leaves and the roots, and lower in the flowers. DDF2 has a similar expression profile (Magome et al., 2004).

ddf1 mutants:

  • The ddf1 mutants are GA-deficient:

The ddf1 mutants are dwarfed and have dark green leaves, which is a phenotype common to some GA-deficient mutants (such as ga1-3) as well as GA-insensitive mutants (such as gai). The ddf1 mutants are late-flowering in both long days and short days, but the late-flowering phenotype is more marked in long days. The mutation is dominant.

The ddf1 mutants contain low levels of endogenous bioactive GAs, but exogenous GA treatment suppresses the mutant phenotype, so they are not insensitive to GAs (Magome et al., 2004).

This inhibition of GA biosynthesis is partial, as ddf1 mutants still contain low levels of endogenous GAs, and are still able to flower in short days (Magome et al., 2004).

  • DDF1 is an inhibitor of flowering:

The ddf1 mutant phenotype seems to be caused by an over-expression of DDF1, and the ddf1 mutants contains high levels of the DDF1 transcript. This would explain the dominant phenotype of the mutant. Plants over-expressing DDF1 or DDF2 under the control of the 35S promoter have the same phenotype than ddf1 mutants (Magome et al., 2004).