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GENETICS, GENOMICS, AND MOLECULAR EVOLUTION

Characterization of the PHO1 Gene Family and the Responses to Phosphate Deficiency of Physcomitrella patens¹

Département de Biologie Moléculaire Végétale, Biophore, Université de Lausanne, CH–1015 Lausanne, Switzerland

PHO1 was previously identified in Arabidopsis (Arabidopsis thaliana) as a protein involved in loading inorganic phosphate (Pi) into the xylem of roots and its expression was associated with the vascular cylinder. Seven genes homologous to AtPHO1 (PpPHO1;1–PpPHO1;7) have been identified in the moss Physcomitrella patens. The corresponding proteins harbor an SPX tripartite domain in the N-terminal hydrophilic portion and an EXS domain in the conserved C-terminal hydrophobic portion, both common features of the plant PHO1 family. Northern-blot analysis showed distinct expression patterns for the PpPHO1 genes, both at the tissue level and in response to phosphate deficiency. Transgenic P. patens expressing the β-glucuronidase reporter gene under three different PpPHO1 promoters revealed distinct expression profiles in various tissues. Expression of PpPHO1;1 and PpPHO1;7 was specifically induced by Pi starvation. P. patens homologs to the Arabidopsis PHT1, DGD2, SQD1, and APS1 genes also responded to Pi deficiency by increased mRNA levels. Morphological changes associated with Pi deficiency included elongation of caulonemata with inhibition of the formation of side branches, resulting in colonies with greater diameter, but reduced mass compared to Pi-sufficient plants. Under Pi-deficient conditions, P. patens also increased the synthesis of ribonucleases and of an acid phosphatase, and increased the ratio of sulfolipids over phospholipids. These results indicate that P. patens and higher plants share some common strategies to adapt to Pi deficiency, although morphological changes are distinct, and that the PHO1 proteins are well conserved in bryophyte despite the lack of a developed vascular system.

² These authors contributed equally to the article.

³ Present address: Division of Biological Sciences, University of California, 9500 Gilman Drive, La Jolla, CA 92093–0116.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Yves Poirer (yves.poirier{at}unil.ch).

www.plantphysiol.org/cgi/doi/10.1104/pp.107.108548

^* Corresponding author; e-mail yves.poirier{at}unil.ch.

Received August 31, 2007; accepted November 18, 2007; published November 30, 2007.

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