A Phosphate Transporter from Medicago truncatula Involved in the Acquisition of Phosphate Released by Arbuscular Mycorrhizal Fungi

Abstract

Many plants have the capacity to obtain phosphate via a symbiotic association with arbuscular mycorrhizal (AM) fungi. In AM associations, the fungi release phosphate from differentiated hyphae called arbuscules, that develop within the cortical cells, and the plant transports the phosphate across a symbiotic membrane, called the periarbuscular membrane, into the cortical cell. In Medicago truncatula , a model legume used widely for studies of root symbioses, it is apparent that the phosphate transporters known to operate at the root-soil interface do not participate in symbiotic phosphate transport. EST database searches with short sequence motifs shared by known phosphate transporters enabled the identification of a novel phosphate transporter from M. truncatula , MtPT4. MtPT4 is significantly different from the plant root phosphate transporters cloned to date. Complementation of yeast phosphate transport mutants indicated that MtPT4 functions as a phosphate transporter, and estimates of the K m suggest a relatively low affinity for phosphate. MtPT4 is expressed only in mycorrhizal roots, and the MtPT4 promoter directs expression exclusively in cells containing arbuscules. MtPT4 is located in the membrane fraction of mycorrhizal roots, and immunolocalization revealed that MtPT4 colocalizes with the arbuscules, consistent with a location on the periarbuscular membrane. The transport properties and spatial expression patterns of MtPT4 are consistent with a role in the acquisition of phosphate released by the fungus in the AM symbiosis.

Knocking on the heaven’s wall: pathogenesis of and resistance to biotrophic fungi at the cell wall

“…It remains to be shown whether the same or different vesicle-trafficking pathways become activated in response to attempted cellular invasion by both classes of fungal microorganisms. In this context, it might be relevant that the expression of the MtPT4 gene occurs exclusively in cells containing arbuscules, suggesting the existence of a specific gene-induction mechanism [57 ]. Thus, one possibility is that different gene-induction pathways contribute to generate vesicle-cargo diversity in pathogenic and symbiotic interactions.…”

“…Fluorescent signals were absent from haustorial complexes, suggesting that the extra-haustorial membrane may either lack any protein or contain proteins that are unique to this membrane. Interestingly, in symbiotic interactions between plants and arbuscular mycorrhizal fungi, elegant work points to an accumulation of specific proteins at the periarbuscular membrane, a probable structural analogue of the extra-haustorial membrane [57 ]. The Medicago truncatula phosphate transporter MtPT4 was shown, by complementation of yeast phosphate transport mutants, to function in phosphate uptake.…”

A Mycorrhizal-Specific Ammonium Transporter from Lotus japonicus Acquires Nitrogen Released by Arbuscular Mycorrhizal Fungi

“…The collection of microdissected cells from mycorrhizal and control roots has allowed us to demonstrate that LjAMT2;2 transcripts are mainly localized in arbusculated cells, as already demonstrated for other transporters (Harrison et al, 2002;Balestrini et al, 2007). The functional characterization of LjAMT2;2 by yeast complementation demonstrates its pH dependency, with the highest uptake rates at acidic pH.…”

“…On the other hand, plants are endowed with Pi transporters that are mycorrhizal specific: their role is to acquire the Pi from the interfacial apoplast and to deliver it to the plant cytoplasm. A Medicago truncatula Pi transporter, described as exclusively expressed during AM symbiosis and located in the periarbuscular membrane (Harrison et al, 2002), is not only essential for the acquisition of the Pi delivered by the AM fungus, but also is required to maintain arbuscules and sustain development of the AM fungus (Javot et al, 2007a).…”

The expression of GintPT, the phosphate transporter of Rhizophagus irregularis, depends on the symbiotic status and phosphate availability

“…As a further step, since the exchange of nutrients is considered the driving force for the evolutionary stability of AM symbiosis (Parniske 2008;Humphreys et al 2010;Kiers et al 2011), we wondered whether the dynamics of the fungal GintPT expression could be related to that of other plant and fungal genes involved in nutrients exchanges. We therefore investigated the MtPT4 gene, encoding a phosphate transporter of Medicago truncatula, which is expressed in arbuscule-containing cells and is responsible for the uptake of Pi released by the fungus in the periarbuscular space (Harrison et al 2002;Javot et al 2007). We also investigated the MST2 gene, the fungal hexose transporter which is possibly involved in C uptake (Helber et al 2011).…”