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Review
. 2019 Feb;47:9-15.
doi: 10.1016/j.pbi.2018.08.001. Epub 2018 Aug 30.

The Makings of a Gradient: Spatiotemporal Distribution of Gibberellins in Plant Development

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Free PMC article
Review

The Makings of a Gradient: Spatiotemporal Distribution of Gibberellins in Plant Development

Annalisa Rizza et al. Curr Opin Plant Biol. .
Free PMC article

Abstract

The gibberellin phytohormones regulate growth and development throughout the plant lifecycle. Upstream regulation and downstream responses to gibberellins vary across cells and tissues, developmental stages, environmental conditions, and plant species. The spatiotemporal distribution of gibberellins is the result of an ensemble of biosynthetic, catabolic and transport activities, each of which can be targeted to influence gibberellin levels in space and time. Understanding gibberellin distributions has recently benefited from discovery of transport proteins capable of importing gibberellins as well as novel methods for detecting gibberellins with high spatiotemporal resolution. For example, a genetically-encoded fluorescent biosensor for gibberellins was deployed in Arabidopsis and revealed gibberellin gradients in rapidly elongating tissues. Although cellular accumulations of gibberellins are hypothesized to regulate cell growth in developing embryos, germinating seeds, elongating stems and roots, and developing floral organs, understanding the quantitative relationship between cellular gibberellin levels and cellular growth awaits further investigation. It is also unclear how spatiotemporal gibberellin distributions result from myriad endogenous and environmental factors directing an ensemble of known gibberellin enzymatic and transport steps.

Figures

Figure 1
Figure 1
Gibberellin biochemistry in Arabidopsis. Model of subcellular localization of gibberellin biosynthetic and catabolic pathways as well as putative intra/intercellular movements of gibberellins. Gibberellin accumulation and depletion steps are depicted with black and red arrows, respectively. Biosynthetic steps occur in the three cellular compartments (plastids, endoplasmic reticulum (ER) and cytoplasm); the corresponding enzymes are reported with the following nomenclature: ent-copalyl diphosphate synthase, CPS; ent-kaurene synthase, KS; ent-kaurene oxidase, KO; ent-kaurenoic acid oxidase, KAO; gibberellin 20-oxidase, GA20ox; gibberellin 3-oxidase, GA3ox. Gibberellin deactivation enzymes convert either precursors or bioactive gibberellins into inactive catabolites. Shown here are members of GA2ox and CYP714A families. Transporters belonging to NPF and SWEET families import extracellular GA4. Potential mechanisms for GA4 export and GA12 transport remain poorly understood.
Figure 2
Figure 2
Gibberellin gradients compared with cellular growth rate in dark grown hypocotyl and root tip. Analysis of nuclear localized GPS1 (nlsGPS1) expressed in Arabidopsis at three days post sowing as described in Ref. [37••]. Comparison of regions of cellular elongation with nlsGPS1 emission ratios in (a) a dark grown hypocotyl and (b) a light grown root. In both tissues, gibberellin levels correlate with cell elongation rate. Scale bars (a) 70 μm (b) 30 μm.
Figure 3
Figure 3
Model of environmental regulation of gibberellin distribution and cell growth in seeds and hypocotyls. (a) Contrasting regulation of gibberellins by light in seeds (left) versus hypocotyls (right). In seeds, the absence of PIF1 protein allows for the accumulation of gibberellins and the inhibition of DELLAs, thereby inducing radicle cell elongation and germination. Accumulation of gibberellins might not correlate with cell elongation [33••]. In hypocotyls, the absence of PIF proteins instead reduces gibberellin levels and promotes DELLA activity, thereby reducing hypocotyl cell elongation. Accumulation of gibberellins again might not correlate with cell elongation [37••]. (b) Contrasting regulation of gibberellins by darkness in seeds (left) versus hypocotyls (right). In seeds, the presence of PIF1 protein reduces gibberellin levels and promotes DELLA activity, thereby inhibiting germination [43,44]. In hypocotyls, the presence of PIF proteins allows for the accumulation of gibberellins and the inhibition of DELLAs, thereby inducing hypocotyl cell elongation. Here, accumulation of gibberellins correlates with cell elongation [37••].

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