Sheerin DJ, Buchanan J, Kirk C, Harvey D, Sun X, Spagnuolo J, Li S, Liu T, Woods VA, Foster T, Jones WT, Rakonjac J

The phytohormone gibberellin and the DELLA proteins act together to control key aspects of plant development. Gibberellin induces degradation of DELLA proteins by recruitment of an F-box protein, using a molecular switch: a gibberellin-bound nuclear receptor interacts with the N-terminal domain of DELLA proteins, and this event primes the DELLA ...

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C-terminal domain for interaction with the F-box protein. However, the mechanism of signalling between the N- and C-terminal domains of DELLA proteins is unresolved. We used in vivo and in vitro approaches to characterise two- and three-partite interactions of the DELLA protein RGL1 of Arabidopsis thaliana with the gibberellin receptor GID1A and the F-box protein SLY1. Deuterium exchange mass spectroscopy unequivocally showed that the RGL1 entire N-terminal domain is disordered prior to interaction with the GID1A; furthermore, association/dissociation kinetics, determined by surface plasmon resonance, predicts a two state conformational change of the RGL1 N-terminal domain upon interaction with GID1A. Additionally, competition assays with monoclonal antibodies revealed that contacts mediated by the short helix Asp/Glu/Leu/Leu of the hallmark DELLA motif are not essential for the GID1A-RGL1 N-terminal domain interaction. Finally, yeast two- and three-hybrid experiments determined that unabated communication between N- and C-terminal domains of RGL1 is required for recruitment of the F-box protein SLY1.

Date: Feb. 15, 2011

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