Arabidopsis Pht1;5 Mobilizes Phosphate between Source and Sink Organs and Influences the Interaction between Phosphate Homeostasis and Ethylene Signaling    

Abstract

Phosphorus (P) remobilization in plants is required for continuous growth and development. The Arabidopsis (Arabidopsis thaliana) inorganic phosphate (Pi) transporter Pht1;5 has been implicated in mobilizing stored Pi out of older leaves. In this study, we used a reverse genetics approach to study the role of Pht1;5 in Pi homeostasis. Under low-Pi conditions, Pht1;5 loss of function (pht1;5-1) resulted in reduced P allocation to shoots and elevated transcript levels for several Pi starvation-response genes. Under Pi-replete conditions, pht1;5-1 had higher shoot P content compared with the wild type but had reduced P content in roots. Constitutive overexpression of Pht1;5 had the opposite effect on P distribution: namely, lower P levels in shoots compared with the wild type but higher P content in roots. Pht1;5 overexpression also resulted in altered Pi remobilization, as evidenced by a greater than 2-fold increase in the accumulation of Pi in siliques, premature senescence, and an increase in transcript levels of genes involved in Pi scavenging. Furthermore, Pht1;5 overexpressors exhibited increased root hair formation and reduced primary root growth that could be rescued by the application of silver nitrate (ethylene perception inhibitor) or aminoethoxyvinylglycine (ethylene biosynthesis inhibitor), respectively. Together, these data indicate that Pht1;5 plays a critical role in mobilizing Pi from P source to sink organs in accordance with developmental cues and P status. The study also provides evidence for a link between Pi and ethylene signaling pathways.

A Constitutive Expressed Phosphate Transporter, OsPht1;1, Modulates Phosphate Uptake and Translocation in Phosphate-Replete Rice

“…In Arabidopsis, overexpression of AtPht1;5 led to increases of root hair numbers and length both under Pi-sufficient and Pi-deficient conditions, while silencing of the gene did not have a significant effect on root hair development (Nagarajan et al, 2011). It was remarkable that the OsPT1-Ri lines, particularly OsPT1-Ox lines, developed much longer and dense root hairs only under P-replete conditions (Fig.…”

“…It has been shown that AtPht1;1 and AtPht1;4, which were most highly expressed in epidermis and root hair cells, contributed to Pi transport into roots during growth in a wide range of external Pi concentrations (Shin et al, 2004), while AtPht1;5, which showed Pi deficiency-induced expression specifically in the phloem cells of older leaves, cotyledons, and flowers (Mudge et al, 2002), functions in mobilizing Pi between source and sink organs (Nagarajan et al, 2011). That the OsPT1 promoter directed its constitutive expression in epidermis, cortex, and stele cells of various rice tissues (Fig.…”

“…The double mutant of both AtPht1;1 and AtPht1;4 showed a 75% reduction in Pi uptake capacity as compared with wild-type plants (Shin et al, 2004). Recently, Nagarajan et al (2011) reported that the Arabidopsis pht1;5-1 mutant had higher shoot P content compared with the wild type, while the P content in roots was reduced under Pi-replete conditions, suggesting that Pht1;5 may mobilize Pi between source and sink tissues. In addition, Preuss et al (2010) explored the characteristics of the low-affinity barley (Hordeum vulgare) PiT PHT1;6 using the Xenopus laevis oocyte expression system, implying that it may play a Pi-transport role at Pi-sufficient conditions in plants.…”

“…A large number of the genes that encode PiTs have been identified from different plant families, including Arabidopsis (Arabidopsis thaliana), cereals, legumes, and solanaceous species (Paszkowski, 2006;Bucher, 2007;Chen et al, 2007;Ai et al, 2009;Jia et al, 2011;Nagarajan et al, 2011). A majority of them showed expression either exclusively or predominantly in the roots, and transcript levels were strongly induced by low Pi supply or by inoculation with arbuscular mycorrhiza (Mudge et al, 2002;Paszkowski et al, 2002;Javot et al, 2007;Ai et al, 2009).…”

Genetic approaches to enhancing phosphorus-use efficiency (PUE) in crops: challenges and directions

“…Loss-of-function mutants of AtPHT1;5 and transgenic lines overexpressing this gene in Arabidopsis were developed to demonstrate its role in Pi mobilisation between source and sink under different Pi conditions (Nagarajan et al 2011). Little is known about the roles of PHT1 genes in P loading into grains in cereals such as wheat and barley.…”