A phosphate transporter expressed in arbuscule-containing cells in potato

Abstract

Arbuscular mycorrhizas are the most common non-pathogenic symbioses in the roots of plants. It is generally assumed that this symbiosis facilitated the colonization of land by plants. In arbuscular mycorrhizas, fungal hyphae often extend between the root cells and tuft-like branched structures (arbuscules) form within the cell lumina that act as the functional interface for nutrient exchange. In the mutualistic arbuscular-mycorrhizal symbiosis the host plant derives mainly phosphorus from the fungus, which in turn benefits from plant-based glucose. The molecular basis of the establishment and functioning of the arbuscular-mycorrhizal symbiosis is largely not understood. Here we identify the phosphate transporter gene StPT3 in potato (Solanum tuberosum). Functionality of the encoded protein was confirmed by yeast complementation. RNA localization and reporter gene expression indicated expression of StPT3 in root sectors where mycorrhizal structures are formed. A sequence motif in the StPT3 promoter is similar to transposon-like elements, suggesting that the mutualistic symbiosis evolved by genetic rearrangements in the StPT3 promoter.

Structure and Expression Profile of the Phosphate Pht1 Transporter Gene Family in Mycorrhizal Populus trichocarpa

“…Both the CTTC and P1BS motifs were present in the PtPT10 promoter sequences of both poplar Nisqually 1 and poplar clone INRA 101-74 in the same subregion. Moreover, the PtPT10 promoter sequence has three motifs out of 13 (TGTATTGATTTT, GTATT-GATTTTT, and ATTTTAAAAAAA) similar with those from MtPT4 and StPT4 as well as a motif (CAAT-TATTT at 21,049) very similar to the motif reported in StPT3 (CAATTATTG at 21,227; Rausch et al, 2001).…”

“…Wild-type and transformant potato plants (Solanum tuberosum var Désirée) containing the 1.7-kb pStPT3::GUS construct (Rausch et al, 2001) were propagated in vitro in glass jars (E+H Services AG Däniken) in 23 MS medium in a growth chamber. The plants were then used for the generation of hairy roots in vitro or transferred to a miniature greenhouse for mycorrhizal experiments (Supplemental Materials and Methods S1).…”

“…The first described AM-inducible Pi transporter gene, StPT3 from potato (Solanum tuberosum), encodes a high-affinity Pi transporter (Rausch et al, 2001). The 1.7-kb-long StPT3 promoter directed GUS expression specifically in cortex cells harboring arbuscules and coiled hyphae in transgenic roots of several herbaceous plant species, including potato, Petunia hybrida, Daucus carota, Medicago truncatula, and Lotus japonicus (Rausch et al, 2001;Karandashov et al, 2004), indicating evolutionary conservation of gene regulatory mechanisms in symbiotic Pi transport of distantly related plant species.…”

Symbiotic Status, Phosphate, and Sucrose Regulate the Expression of Two Plasma Membrane H+-ATPase Genes from the Mycorrhizal Fungus Glomus mosseae

“…These are branched hyphae with a very thin wall, surrounded by apoplastic space and by the periarbuscular membrane formed by invagination of the plant plasma membrane. There is increasing evidence that phosphate, translocated from the soil through the fungus, is downloaded at the arbuscule interface where it is taken up by plant transporters (Rosewarne et al, 1999;Rausch et al, 2001). In contrast, little is known about where the exchange of carbon takes place.…”

Peace Talks and Trade Deals. Keys to Long-Term Harmony in Legume-Microbe Symbioses

“…In mycorrhizal roots, phosphate is acquired by the extraradical fungal hyphae and is then transferred to the arbuscules, where it is released from the fungus and transported across the periarbuscular membrane into the cortical cell. In the past few years, there has been progress in understanding the molecular basis of phosphate transport in the symbiosis, and, most recently, plant phosphate transporters implicated in the uptake of phosphate released from the arbuscule have been reported (Rausch et al, 2001;Harrison et al, 2002;Paszkowski et al, 2002). In potato (Solanum tuberosum), expression of a high-affinity phosphate transporter, StPT3, is induced in mycorrhizal roots, particularly in cells containing arbuscules, making it a strong candidate for involvement in symbiotic phosphate transport (Rausch et al, 2001).…”