PHOSTASIA

Phosphate transport and signaling in Arabidopsis

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 Obiettivo del progetto (Objective)

'Phosphate (Pi)-based fertilizers are essential to agriculture but are a non-renewable resource and a major cause of water pollution. Understanding how plants sense and adapt to Pi deficiency is key to attain sustainable agriculture. Contrary to Pi import, mechanisms regulating Pi export are unknown despite being essential for Pi homeostasis in most eukaryotes (e.g. human kidney or mychorizzal roots). The only protein known to mediate Pi efflux is the Arabidopsis thaliana PHO1. PHO1 mediates Pi efflux when expressed in Xenopus oocytes and is responsible for loading Pi into the root xylem. PHO1 is also involved in Pi deficiency signaling, linking low Pi to reduced growth and gene activation. PHO1 has thus a dual function in transport and signaling, a feature typical of transceptors. The protein contains two distinct domains, called SPX and EXS, and is localized to endosomes. Plant PHO1 homologues have functions other than Pi homeostasis; PHO1;H4 (SHB1) is associated with the nucleus and modulates hypocotyl growth under blue light. This project aims on a detailed structure-function analysis of PHO1 to determine; 1- its topology in endosomes; 2- the domains responsible for Pi export, Pi signaling, and the distinct sub-cellular localization and function of PHO1 and PHO1;H4, 3- the role of phosphorylation on PHO1 localization and activity. Membrane topology will be determined by bimolecular fluorescence and redox-sensitive GFP. Mutagenized and truncated versions of PHO1, as well as chimeras between PHO1 and PHO1;H4 will be expressed, their localization determined by confocal and two-photon microscopy, and their Pi export activity performed in Xenopus oocytes and plants. Signal transduction for Pi deficiency and blue light will be determined by growth assays and gene expression profiling. The information will be transferred to other PHO1-family members with poorly determined function, such as the human XRP1 and other plant proteins containing SPX or EXS domains.'

Introduzione (Teaser)

Researchers have investigated phosphate-transporting proteins in both plants and animals. Phosphate metabolism is key to modern agriculture.

Descrizione progetto (Article)

Phosphate-based fertilisers have revolutionised agriculture in modern times, allowing improved growth and maximising crop yield. However, phosphate run-off from fields is one of the major water pollutants in the world today.

Despite the importance of phosphates in agriculture, little is known about the mechanisms of phosphate import and export in plants. The EU-funded 'Phosphate transport and signaling in Arabidopsis' (PHOSTASIA) project aimed to investigate the role of PHO1, a phosphate transporter and signalling protein in Arabidopsis thaliana.

The project began by determining the structure of PHO1 for the first time. This knowledge allowed researchers to create various mutated forms of PHO1 in order to better understand how the protein works.

Scientists also used genetic engineering to create an A. thaliana plant that grew normally despite having low phosphate concentrations in its shoots.

Another aspect of the project found that expression of the mammalian PHO1 orthologue XPR1 in tobacco leads to export phosphate out of cells, making it the first phosphate exporter identified in mammals.

PHOSTASIA has advanced our knowledge of phosphate transport in both plants and animals. This will ultimately contribute to the sustainable use of phosphate in agriculture.