Submitted to: Plant Physiology
Publication Type: Review Article
Publication Acceptance Date: 7/24/2012
Publication Date: 9/1/2012
Citation: Hauvermale, A.L., Ariizumi, T., Steber, C.M. 2012. Gibberellin signaling: a theme and variations on DELLA repression. Plant Physiology. 160:83-92 Available: http://www.plantphysiol.org/content/160/1/83. Interpretive Summary: This review article was invited by the editors of Plant Physiology with page charges waived. It was subject to complete peer-review prior to acceptance. This paper reviews recent advances in understanding the mechanisms of GA signaling, especially as they relate to a plant's ability to respond and adapt to its environment. The paper reviews current literature and proposes new models that integrate old and new research about GA signaling. Of particular interest is the fact that the DELLA repressor of GA responses interacts with multiple protein targets to control plant growth and development in terms of stem elongation, cell division, seed germination, flowering, cold tolerance and pathogen response.
Technical Abstract: DELLA proteolysis through the ubiquitin-proteasome pathway or through the proteolysis-independent mechanisms. GA triggers DELLA proteolysis via a series of protein-protein interactions. GA binding to the GID1 GA receptor increases the affinity of GID1 for DELLA leading to the formation of the GID1-GA-DELLA complex. SLY1/GID2 is an F-box subunit of an SCF E3 ubiquitin ligase. Formation of the GID1-GA-DELLA complex increases the affinity of SLY1/GID2 for DELLA resulting in DELLA polyubiquitination, the addition of a covalently linked chain of ubiquitin polypeptides to DELLA. Polyubiquitination causes DELLA recognition proteolysis by the 26S proteasome. DELLA destruction lifts repression of seed germination, stem elongation, cell division, and flowering. DELLA repression can also be lifted by GID1-GA-DELLA complex formation alone in mutants lacking the SLY1/GID2 F-box protein, and apparently by either phosphorylation or lack of modification by the SPY O-GlcNAc transferase. Recent studies have suggested that DELLA represses GA responses by protein-protein interactions with multiple transcriptional activators and repressors. For example, DELLA binding prevents PHYTOCHROME INTERACTING FACTOR4 (PIF4) from binding to its target promoters thereby preventing PIF4-stimulated hypocotyl growth. DELLA also negatively regulates JAZ1 thereby preventing JAZ1 repression of wounding/pathogen responses, and negatively regulates SCL3 to block root growth, shoot growth, flowering, and seed germination. Thus, DELLA proteins have the ability to bind a wide variety of protein targets enabling GA to regulate multiple developmental and growth responses to the environment.