DELLA Proteins in Signalling

Abstract

DELLAs are a family of nuclear proteins that act as growth repressors throughout the life cycle of higher plants. Derepression is mediated through the gibberellic acid (GA)‐dependent degradation of DELLAs and the key components of the GA‐DELLA signalling pathway (the GA receptor and the F‐box protein involved in DELLA destruction) have recently been identified. It is becoming increasingly clear that DELLAs promote a plant's survival by integrating its growth responses to a wide range of endogenous and environmental signals.

Keywords: gibberellin (GA); growth repressor; receptor; proteasome; phytohormones

Figure 1.

The phenotype of wild type and GA‐deficient Arabidopsis plants. The GA1 gene encodes a GA biosynthetic enzyme, copalyl diphosphate synthase and the ga1‐3 mutation results in extremely low levels of endogenous GA. In this mutant DELLA proteins are stabilized resulting in its dark‐green dwarf phenotype. Introducing knockout mutations into specific DELLA genes in this background allows their function to be investigated. Each pot contains four plants which were grown under short‐day conditions for 8 weeks. WT=wild type.

Figure 2.

Schematic representation of the conserved domains of the DELLA proteins. The conserved domains are indicated by the filled boxes. Boxes infilled in green in the N‐terminal region of the protein indicate domains present only in DELLA proteins, whereas the five GRAS motif designations are shown in blue. The DELLA‐specific domains (DELLA and TVHYNP, also known as domains I and II, respectively) are required for GA signalling whereas the C‐terminal domain has a repressor function. The Arabidopsisgai and wheat Rht‐B1b and Rht‐D1b mutations have, respectively, a 17‐amino acid deletion beginning at the first amino acid (D) of the DELLA motif, or translational stop codons at the end of the DELLA (domain I) domain.

Figure 3.

Phenotype of wild type (WT) and quadruple‐DELLAArabidopsis plants. Quadruple DELLA plants have knockout mutations in GAI, RGA, RGL1 and RGL2, but have a functional RGL3 gene. These plants have a phenotype similar to WT plants treated with GA, they show reduced seed dormancy and early flowering, particularly when grown in short‐day photoperiods. In this image, plants were grown for 9 weeks in short‐day conditions. quad‐DELLA=quadruple DELLA mutant.

Figure 4.

The phenotype of WT, gain‐of‐function (GoF) and loss‐of‐function (LoF) mutants of barley. GoF mutants containing a mutation within the DELLA domain resulting in stabilization of the DELLA protein, exhibit a dark‐green dwarf phenotype with increased tillering compared to WT plants. LoF mutants exhibit a GA‐constitutive phenotype (plants are light green, tall and slender with reduced tillering); the mutation is located in the C‐terminal (repressor) region of SLN1. The WT and the GoF mutant plants are fertile, but the LoF mutant is male sterile.

Figure 5.

The GA‐DELLA signalling mechanism. In the absence of GA, the DELLA proteins are stabilized in the nucleus and repress DELLA‐mediated growth, presumably via modulation of transcription of target genes. In the presence of GA, GA binds to the soluble GID1 receptor. In the nucleus the GA‐GID1 complex associates with the DELLA proteins, promoting a further interaction between DELLA and the SCFSLY1/GID2 complex. The SCF complex catalyses the polyubiquitination of the DELLA protein, triggering DELLA degradation by the 26S proteasome. Destruction of the DELLA protein derepresses the DELLA‐mediated growth restraint and allows growth to occur.

Figure 6.

DELLA proteins are integrators of multiple phytohormone and signalling pathways. The DELLA proteins restrain plant growth; restraint is released by degradation of the protein(s) by GA‐triggered DELLA degradation. The DELLAs integrate information from multiple signalling pathways; all of the pathways and stresses illustrated have been shown to alter the abundance/stability of DELLAs. It is suggested that DELLAs affect biotic stress responses by modulating the jasmonic acid/ethylene‐mediated defence signalling pathways. ? denotes the potential for involvement of additional pathways which may affect GA abundance or impinge directly on DELLA accumulation.

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References

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Further Reading

Achard P, Cheng H, De Grauwe L et al. (2006) Integration of plant responses to environmentally activated phytohormonal signals. Science 311: 91–94.

Olszewski N, Sun T‐P and Gubler F (2002) Gibberellin signalling: biosynthesis, catabolism, and response pathways. Plant Cell 14(suppl.): S61–S80.

Penfield S, Gilday AD, Halliday KJ and Graham IA (2006) DELLA‐mediated cotyledon expansion breaks coat‐imposed seed dormancy. Current Biology 16: 2366–2370.

Thomas SG and Sun T‐P (2004) Update on gibberellin signalling. A tale of the tall and the short. Plant Physiology 135: 668–676.

Tyler L, Thomas SG, Hu J et al. (2004) DELLA proteins and gibberellin‐regulated seed germination and floral development in Arabidopsis. Plant Physiology 135: 1008–1019.

Yasumura Y, Crumpton‐Taylor M, Fuentes S and Harberd NP (2007) Step‐by‐step acquisition of the gibberellin‐DELLA growth‐regulatory mechanism during land‐plant evolution. Current Biology 17: 1225–1230.

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How to Cite close
Alvey, Liz, and Boulton, Margaret I(Jul 2008) DELLA Proteins in Signalling. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0020096]