Regulation of flowering time in Arabidopsis



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Flowering pathway

Gibberellin pathway



The Gibberellin transduction pathway


Interaction between GI and SPY


The SPY/GI protein interaction:

  • SPY is able to interact with GI: Sothern et al. (2002) indicated that SPY seemed to be controlled by the clock. Subsequent yeast 2-hybrid system experiments have show that the TPR domain of SPY is able to directly interact with GI (Tseng et al., 2004). Although this has not yet been observed in planta, it may be due to the low abundance of both proteins.

  • The spy-2/spy-2 interaction is weaker than in the WT, but the spy-2/GI interaction is stronger: In the spy-2 mutant, portions of the TPR domains are deleted. As a result, the spy-2/spy-2 interaction is weakened (See Tseng et al., 2001 and here), but the interaction between the spy-2 mutant protein and GI is stronger, compared to SPY/GI (Tseng et al., 2004).

Analysis of the possible interaction between GI and SPY:

Without GA treatment, spy-4 flowers early. The photoperiod pathway mutants gi-3, co-2 and ft-1 flower late, and all the double mutants gi-3 spy-4, co-2 spy-4 and ft-1 spy-4 flower at intermediate times. GA treatment entirely complements the spy-4 mutant phenotype. It also accelerates flowering in the gi-3, co-2 and ft-1 single mutants, although they remain late-flowering. However, GA treatment does not accelerate flowering in the double mutants. This means that the spy-4 mutation suppresses more effectively the gi-3 mutation than does the GA treatment, which indicates that SPY also belongs to the photoperiod pathway (Tseng et al., 2004).

This interaction between SPY and GI may be one of the several possible connections between the GA transduction pathway and the photoperiod pathway.