The phytochrome (phy) system enables plants to adapt to canopy shade. By sensing the reduction of the red:far-red light ratio in shade, phyA and phyB trigger downstream signalling cascades which eventually lead to enhanced elongation growth. In this study, we show that the F-box protein EID1 takes on an essential function within the shade avoidance response in Arabidopsis thaliana by repressing phyA action and thereby allowing seedlings to elongate in shade. Thus, altering EID1 activity provides a means to adapt the shade response without affecting phyB action and could have played a role in the evolution of shade tolerance.
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