Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 7/18/2009
Publication Date: 7/18/2009
Publication URL: http://www.aspb.org/meetings/pb-2009
Citation: Ariizumi, T., Steber, C.M. 2009. Relieving DELLA Repression of Stem Elongation and Flowering, Evidence for a Proteolysis Independent Mechanism for GA signaling. Meeting Abstract. www.aspb.org/meetings/pb-2009. Interpretive Summary:
Technical Abstract: GA stimulates germination, stem elongation, and flowering by lifting DELLA protein repression of these responses via both proteolysis dependent and independent pathways. There are five members of the DELLA protein family in Arabidopsis with partially overlapping functions. GA biosynthesis lifts DELLA repression by triggering DELLA proteolysis via the ubiquitin-proteasome pathway. Perception of GA by the GA receptors GIBBERELLIN INSENSITIVE DWARF1 (GID1a, b, and c) enables GID1/GA to recognize and bind the DELLA protein. It appears that the SLY1 protein binds and ubiquitinates DELLA only when it is in the GID1/GA/DELLA complex. Polyubiquitinaiton by the SCF-SLY1 E3 ubiquitin ligase then targets DELLA for proteolysis. If DELLA proteolysis were the only mechanism for DELLA inactivation, then the level of DELLA protein should correlate with the degree of dwarfism and other GA phenotypes. In contrast, sly1 mutants accumulate more DELLA protein but display less severe dwarf and germination phenotypes than the GA biosynthesis mutant ga1-3 or the gid1abc triple mutant. Interestingly, GID1 overexpression rescued the sly1 dwarf and infertility phenotypes without decreasing the accumulation of the DELLA protein REPRESSOR OF GA1-3 (RGA). GID1 rescue of sly1 mutants appeared to be dependent on the level of GID1 protein, GA, and the presence of a functional DELLA motif. Since DELLA shows increasing protein interaction with GID1 with increasing GA levels in vivo, it appears that GA-bound GID1 can block DELLA repressor activity by direct protein interaction with the DELLA domain. Thus, a SLY1 independent mechanism for GA signaling may function without DELLA degradation.