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Gibberellin-deactivating GA2OX enzymes act as a hub for auxin-gibberellin crosstalk in Arabidopsis thaliana root growth regulation

ABSTRACT: We combined transcriptomic profiling of auxin related mutants with genetic and biochemical approaches and live-cell imaging techniques of Arabidopsis roots to understand the role of auxin-driven gibberellin level changes during root development, particularly root cell elongation. We show that auxin negatively regulates the level of gibberellin in root elongation zone. Auxin signalling steers the expression of gibberellin deactivating enzymes - GIBBERELLIN 2-OXIDASES (GA2OX) exclusively in root elongation zone. Interestingly, GA2OX8 expression is high in tissues with elevated auxin levels, such as vasculature or stem cell niche, fitting with the observed effect of auxin on gibberellin level. Here we show that GA2OX enzymes are negative regulators of root cell elongation. Gibberellin decrease caused by GA2OX8 overexpression inhibits root cell elongation. In contrast, roots missing GA2OX genes elongate faster. These findings indicate that GA2OX8 enzymes represent an integration core of auxin and gibberellin signalling pathway in root elongation zone, vascular development and regulation of stem cell niche. Our results enhance understanding of complex mechanisms controlling root cell elongation.

ORGANISM(S): Arabidopsis thaliana

PROVIDER: GSE282145 | GEO | 2024/12/31

REPOSITORIES: GEO

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Project description:This model is from the article: The influence of cytokinin-auxin cross-regulation on cell-fate determination in Arabidopsis thaliana root development Muraro D, Byrne H, King J, Voss U, Kieber J, Bennett M. J Theor Biol.2011 Aug 21;283(1):152-67. PMID: 21640126, Abstract: Root growth and development in Arabidopsis thaliana are sustained by a specialised zone termed the meristem, which contains a population of dividing and differentiating cells that are functionally analogous to a stem cell niche in animals. The hormones auxin and cytokinin control meristem size antagonistically. Local accumulation of auxin promotes cell division and the initiation of a lateral root primordium. By contrast, high cytokinin concentrations disrupt the regular pattern of divisions that characterises lateral root development, and promote differentiation. The way in which the hormones interact is controlled by a genetic regulatory network. In this paper, we propose a deterministic mathematical model to describe this network and present model simulations that reproduce the experimentally observed effects of cytokinin on the expression of auxin regulated genes. We show how auxin response genes and auxin efflux transporters may be affected by the presence of cytokinin. We also analyse and compare the responses of the hormones auxin and cytokinin to changes in their supply with the responses obtained by genetic mutations of SHY2, which encodes a protein that plays a key role in balancing cytokinin and auxin regulation of meristem size. We show that although shy2 mutations can qualitatively reproduce the effect of varying auxin and cytokinin supply on their response genes, some elements of the network respond differently to changes in hormonal supply and to genetic mutations, implying a different, general response of the network. We conclude that an analysis based on the ratio between these two hormones may be misleading and that a mathematical model can serve as a useful tool for stimulate further experimental work by predicting the response of the network to changes in hormone levels and to other genetic mutations.

Project description:Previous work showed that the maize primary root adapts to low water potential (-1.6 MPa) by maintaining longitudinal expansion in the apical 3 mm (region 1), whereas in the adjacent 4 mm (region 2) longitudinal expansion reaches a maximum in well-watered roots but is progressively inhibited at low water potential. To identify mechanisms that determine these responses to low water potential, transcript expression was profiled in these regions of water-stressed and well-watered roots. In addition, comparison between region 2 of water-stressed roots and the zone of growth deceleration in well-watered roots (region 3) distinguished stress-responsive genes in region 2 from those involved in cell maturation. Responses of gene expression to water stress in regions 1 and 2 were largely distinct. The largest functional categories of differentially expressed transcripts were reactive oxygen species and carbon metabolism in region 1, and membrane transport in region 2. Transcripts controlling sucrose hydrolysis distinguished well-watered and water-stressed states (invertase vs. sucrose synthase), and changes in expression of transcripts for starch synthesis indicated further alteration in carbon metabolism under water deficit. A role for inositols in the stress response was suggested, as was control of proline metabolism. Increased expression of transcripts for wall-loosening proteins in region 1, and for elements of ABA and ethylene signaling were also indicated in the response to water deficit. The analysis indicates that fundamentally different signaling and metabolic response mechanisms are involved in the response to water stress in different regions of the maize primary root elongation zone. Keywords: water stress response, root growth Three pair-wise comparisons were made of transcripts from water-stressed and well-watered tissues in the different root tip regions. In the first comparison (C1), transcripts from region 1 of water-stressed seedlings were compared with those from region 1 of well-watered seedlings. The second comparison (C2) was made between transcripts from region 2 of the two treatments. We expected a larger number of genes to be differentially expressed in region 2 because its elongation rate decreased greatly under water-stressed compared with well-watered conditions. To prioritize the differentially expressed genes revealed in this comparison, a distinction was made between those genes that are associated with growth inhibition in region 2 specifically as a response to water stress, and those genes that are involved in root cell maturation whether under stress or control conditions. A hypothetical example of the former might be genes involved in auxin response since water stress can increase maize root auxin content [8] and application of exogenous auxin can shorten the root growth zone [9]. An example of the latter might involve genes for secondary wall synthesis, e.g., [10]. To experimentally make this distinction a third pair-wise comparison (C2/3) was included to compare expression of genes between water-stressed region 2 and well-watered region 3 as these are both regions of cell maturation. Genes differentially expressed in both C2 and C2/3 are more likely to cause growth inhibition at low water potential and are not likely to be part of the maturation program itself, whereas genes differentially expressed only in C2 are more likely related to maturation. Four biological replicates were included each with dye-swap. The maize oligonucleotide array comes in two slides, A and B. Thus for each of the three comparisons made there were 16 slides (4 biological reps, 2 for dye-swap, 2 parts to an array).

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Gibberellin-deactivating GA2OX enzymes act as a hub for auxin-gibberellin crosstalk in Arabidopsis thaliana root growth regulation

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