Coordination between zinc and phosphate homeostasis involves the transcription factor PHR1, the phosphate exporter PHO1, and its homologue PHO1;H3 in Arabidopsis.

Ghazanfar Abbas Khan,Yves Poirier,Samir Bouraine,Hatem Rouached,Matthieu De Carbonnel,Pierre Berthomieu,Yuanyuan Li,Stefanie Wege

doi:10.1093/jxb/ert444

Abstract

Interactions between zinc (Zn) and phosphate (Pi) nutrition in plants have long been recognized, but little information is available on their molecular bases and biological significance. This work aimed at examining the effects of Zn deficiency on Pi accumulation in Arabidopsis thaliana and uncovering genes involved in the Zn-Pi synergy. Wild-type plants as well as mutants affected in Pi signalling and transport genes, namely the transcription factor PHR1, the E2-conjugase PHO2, and the Pi exporter PHO1, were examined. Zn deficiency caused an increase in shoot Pi content in the wild type as well as in the pho2 mutant, but not in the phr1 or pho1 mutants. This indicated that PHR1 and PHO1 participate in the coregulation of Zn and Pi homeostasis. Zn deprivation had a very limited effect on transcript levels of Pi-starvation-responsive genes such as AT4, IPS1, and microRNA399, or on of members of the high-affinity Pi transporter family PHT1. Interestingly, one of the PHO1 homologues, PHO1;H3, was upregulated in response to Zn deficiency. The expression pattern of PHO1 and PHO1;H3 were similar, both being expressed in cells of the root vascular cylinder and both localized to the Golgi when expressed transiently in tobacco cells. When grown in Zn-free medium, pho1;h3 mutant plants displayed higher Pi contents in the shoots than wild-type plants. This was, however, not observed in a pho1 pho1;h3 double mutant, suggesting that PHO1;H3 restricts root-to-shoot Pi transfer requiring PHO1 function for Pi homeostasis in response to Zn deficiency.

Highlights

Plants require phosphorus (P) and zinc (Zn) to ensure various basic biological functions and complete their life cycle (Poirier and Bucher, 2002; Sinclair and Krämer, 2012)
In order to determine the effect of Zn deficiency on Pi distribution in Arabidopsis tissues, plants were grown in media with either low Zn (0 μM Zn) or low Pi (10 μM Pi) and compared to those grown on complete medium (1 mM Pi and 15 μM Zn)
It is expected that a certain level of coordination and crosstalk must exist between pathways involved in Pi and Zn transport and signalling in plants, key genes acting in this coordination still remain to be identified

Summary

Introduction

Plants require phosphorus (P) and zinc (Zn) to ensure various basic biological functions and complete their life cycle (Poirier and Bucher, 2002; Sinclair and Krämer, 2012). Overaccumulation of Pi in response to Zn deficiency might partially be the result of a specific induction of the expression and activity of Pi transporters (Huang et al, 2000). Taken together, these data indicate that Zn-deficient plants appear to have lost the capacity to downregulate the expression of high-affinity Pi transporters in roots despite the presence of an adequate Pi supply (Huang et al, 2000). In Arabidopsis, a recent report by Jain et al (2013) showed that Zn starvation causes a repression and induction of the expression of PHT1;1 in roots and shoots, respectively

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