Poster: Signaling, long distance

Abs # 455: Ethylene regulates Arabidopsis development via the modulation of DELLA protein growth repressor function

Presenter:	Achard, Patrick , patrick.achard@bbsrc.ac.uk
Authors	Achard, Patrick  (A)   Vriezen, Wim H (B)   Van Der Straeten, Dominique  (B)   Harberd, Nicholas P. (A)
Affiliations:	(A): John Innes Centre (B): Department of Molecular genetics, Ghent University

Phytohormones regulate plant development via a poorly understood signal-response network. Ethylene promotes the so-called ‘triple response’: an exaggeration of the transient developmental structure known as the apical hook, together with an inhibition of hypocotyl and root extension growth. The triple response is thought to protect the shoot and root apical meristems from damage during growth through the soil. Gibberellin (GA) regulates the growth and development of plants by overcoming the repressive effects of the DELLA proteins, a family of nuclear repressors of GA response. Recent results indicate that GA-mediated destabilization of DELLA proteins involves GA-stimulated phosphorylation, polyubiquitination via a specific SCF E3 ubiquitin ligase complex and destruction in the 26S proteasome. Although it has long been clear that both ethylene and GA regulate plant growth, it was not clear how their respective signalling pathways interact with one another in growth regulation. Recent experiments have shown that auxin promotes root growth by modulating DELLA protein function. Here we show that the ethylene signalling pathway also regulates growth by modulating the growth-repressing effects of DELLA proteins. We show that ethylene inhibits the growth of roots via the DELLA proteins GAI and RGA, and that ethylene delays the progress of GA-induced disappearance of RGA via a CONSTITUTIVE TRIPLE RESPONSE (CTR1)-dependent signalling pathway. We also show that GA-promoted relief of the growth restraint imposed by GAI and RGA is necessary for apical hook maintenance. Our observations indicate that DELLA proteins act as integrators of multiple phytohormone signal inputs (Ethylene, auxin and GA), coordinating the elongation and differential growth of plant cells.