Low phosphate signaling induces changes in cell cycle gene expression by increasing auxin sensitivity in the Arabidopsis root system

Laboratorio Nacional de Genómica para la Biodiversidad, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Irapuato, Guanajuato México.
Plant signaling & behavior 08/2009; 4(8):781-3. DOI: 10.4161/psb.4.8.9230
Source: PubMed


Lateral root development is an important morphogenetic process in plants, which allows the modulation root architecture and substantially determines the plant's efficiency for water and nutrient uptake. Postembryonic root development is under the control of both endogenous developmental programs and environmental stimuli. Nutrient availability plays a major role among environmental signals that modulate root development. Phosphate (Pi) limitation is a constraint for plant growth in many natural and agricultural ecosystems. Plants possess Pi-sensing mechanisms that enable them to respond and adapt to conditions of limited Pi supply, including increased formation and growth of lateral roots. Root developmental modifications are mainly mediated by the plant hormone auxin. Recently we showed that the alteration of root system architecture under Pi-starvation may be mediated by modifications in auxin sensitivity in root cells via a mechanism involving the TIR1 auxin receptor. In this addendum, we provide additional novel evidence indicating that the low Pi pathway involves changes in cell cycle gene expression. It was found that Pi deprivation increases the expression of CDKA, E2Fa, Dp-E2F and CyCD3. In particular, E2Fa, Dp-E2F and CyCD3 genes were specifically upregulated by auxin in Pi-deprived Arabidopsis seedlings that were treated with the auxin transport inhibitor NPA, indicating that cell cycle modulation by low Pi signaling is independent of auxin transport and dependent on auxin sensitivity in the root.

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    • "In order to increase Pi uptake, plants have evolved different strategies, such as the enhanced growth of lateral roots and root hairs, and/or the solubilization of soil Pi by means of organic acid and phosphatase secretion: all these processes are probably orchestrated by a systemic signalling that is triggered during Pi starvation (Doener 2008; Lambers et al. 2011; Péret et al. 2011) and involves specific gene expression regulators, as has been demonstrated in Arabidopsis (Pérez Torres et al. 2009). Another widespread and evolutionary ancient strategy is the establishment of arbuscular mycorrhizal (AM) symbiosis which involves the majority of land plants and fungi belonging to the Glomeromycota phylum (Parniske 2008; Bonfante and Genre 2010). "
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    ABSTRACT: The development of mutualistic interactions with arbuscular mycorrhizal (AM) fungi is one of the most important adaptation of terrestrial plants to face mineral nutrition requirements. As an essential plant nutrient, phosphorus uptake is acknowledged as a major benefit of the AM symbiosis, but the molecular mechanisms of its transport as inorganic phosphate (Pi) from the soil to root cells via AM fungi remain poorly known. Here we monitored the expression profile of the high-affinity phosphate transporter (PT) gene (GintPT) of Rhizophagus irregularis (DAOM 197198) in fungal structures (spores, extraradical mycelium and arbuscules), under different Pi availability, and in respect to plant connection. GintPT resulted constitutively expressed along the major steps of the fungal life cycle and the connection with the host plant was crucial to warrant GintPT high expression levels in the extraradical mycelium. The influence of Pi availability on gene expression of the fungal GintPT and the Medicago truncatula symbiosis-specific Pi transporter (MtPT4) was examined by qRT-PCR assay on microdissected arbusculated cells. The expression profiles of both genes revealed that these transporters are sensitive to changing Pi conditions: we observed that MtPT4 mRNA abundance is higher at 320 than at 32 μM suggesting that the flow towards the plant requires high concentrations. Taken on the whole, the findings highlight novel traits for the functioning of the GintPT gene and offer a molecular scenario to the models describing nutrient transfers as a cooperation between the mycorrhizal partners.
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    ABSTRACT: Plants develop most organs post-embryonically, which allows the incorporation of environmental information into decisions concerning when and where to produce new organs. This developmental plasticity is evident in the plant root system, which in dicotyledonous plants such as Arabidopsis thaliana is mostly comprised of lateral and adventitious roots that develop along the length of the primary root. The rate of primary root growth and the location, spacing and growth rate of lateral roots are influenced by the availability of environmental cues such as water and nutrients, which can have dramatic effects on the final architecture of the root system. These environmental responses must intersect with the intrinsic developmental programme of the plant, which is responsible for the general formation and maintenance of the root system. The final root system architecture of any plant is then the product of both intrinsic and environmental response pathways. Carbohydrates and plant hormones such as auxin and cytokinins are required for both intrinsic root development and modulating root system architecture in response to different growth conditions, thus facilitating the optimisation of root growth in complex, heterogeneous environments.
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