Phytochrome moves to the nucleus

In some cases phytochrome itself moves to the nucleus in a light-dependent manner.

The PhyB moves to the nucleus in the Pfr form only, and transport is slow (several hrs).

The PhyA can move in the Pfr or the Pr form, and transport is rapid (about 15 min).

Transport of PhyB-GFP is promoted by red light and inhibited by far-red light.

Transport of PhyA-GFP is maximized under continuous far-red light.

Nuclear translocation of PhyB is under circadian control.

Phytochrome moves to the nucleus

PIF3 (phytochrome interacting fator3)

What Happens when Pfr moves to the nucleus?

Phytochrome Acts though Multiple Signal Transduction Pathways.

G-protein may function downstream of phtochrome. (microinjection experiment)

After G-Protein, there are at least two branching pathways.

1) Gene and chloroplast development : require Ca2+ and calmodulin

2) Anthocyanin synthesis : is independent on Ca2+

3) cGMP may serve as a second messenger in phytochrome action.

Phytochrome is now known to be a protein kinase.

One potential target is a cytosolic protein termed PKS1 that can accept a P from PhyA.

OX of PKS1 suggest that is may function to negatively regulate PHyB mediated events

NDPK2

NDPK2 is another protein kinase associated with phytochrome.

Iys kinase activity is increaseb about 2-fold when PhyA is bound in the Pfr form.

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