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Title: Gibberellin Signaling: a Wake-up Call for Seed Germination

Author
item ARIIZUMI, TOHRU - Washington State University
item Steber, Camille

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 7/18/2010
Publication Date: 7/18/2010
Citation: Ariizumi, T., Steber, C.M. 2010. Gibberellin Signaling: a Wake-up Call for Seed Germination. Meeting Abstract. www.york.ac.uk/org/cnap/ISSS/ISSSseeddormancy.html.

Interpretive Summary:

Technical Abstract: Making an appropriate decision to germinate is essential for the survival of plant species and is important for proper stand establishment in crop plants. Germination is regulated by the antagonistic effects to two plant hormones in Arabidopsis thaliana: abscisic acid (ABA) induces dormancy and represses seed germination, whereas gibberellins (GA) are required for seed germination and stimulation of post-germination processes. Epistasis analyses have shown that ABA acts downstream of GA to repress seed germination. The GA receptor, GID1 (GA-INSENSITIVE DWARF1) stimulates seed germination via negative regulation of DELLA proteins. There are five Arabidopsis proteins that contain the conserved DELLA amino acid sequence and that serve as negative regulators of GA responses including seed germination, stem elongation, and the transition to flowering. GA-binding causes the GID1 receptor to bind DELLA protein, thereby increasing the affinity of DELLA for the F-box protein SLY1. SLY1 is part of an SCF E3 ubiquitin ligase that poly-ubiquitinates DELLA thereby targeting DELLA for destruction by the 26S proteasome. DELLA destruction stimulates seed germination. Mutations in SLY1 cause an increase in seed dormancy that correlates with the severity of the lesion in the gene. The sly1-2 mutant has strong seed dormancy, but this seed dormancy phenotype can be rescued either by long after-ripening or by overexpression of the GA receptor, GID1b. Neither of these germination-stimulating conditions result in a decrease in DELLA protein levels. Thus, there must be both SLY1-dependent and -independent mechanisms for relieving DELLA-repression of seed germination.