Plant phosphorus acquisition in a common mycorrhizal network: regulation of phosphate transporter genes of the Pht1 family in sorghum and flax

Abstract

SummaryIn a preceding microcosm study, we found huge differences in phosphorus (P) acquisition in sorghum (Sorghum bicolor) and flax (Linum usitatissimum) sharing a common mycorrhizal network (CMN). Is the transcriptional regulation of arbuscular mycorrhizal (AM)-induced inorganic orthophosphate (Pi) transporters responsible for these differences?We characterized and analyzed the expression of Pi transporters of the Pht1 family in both plant species, and identified two new AM-inducible Pi transporters in flax.Mycorrhizal Pi acquisition was strongly affected by the combination of plant and AM fungal species. A corresponding change in the expression of two AM-inducible Pht1 transporters was noticed in both plants (SbPT9, SbPT10, LuPT5 and LuPT8), but the effect was very weak.Overall, the expression level of these genes did not explain why flax took up more Pi from the CMN than did sorghum. The post-transcriptional regulation of the transporters and their biochemical properties may be more important for their function than the fine-tuning of their gene expression.

Regulation of plants' phosphate uptake in common mycorrhizal networks: Role of intraradical fungal phosphate transporters

“…7,8 In order to study the mycorrhiza-induced Pht1 genes in flax and sorghum, we characterized and analyzed the expression of Pi transporters of the Pht1 family in both plant species, and identified a set of mycorrhiza-inducible Pi transporters in both plants. 4 Although mycorrhizal Pi acquisition was strongly affected by AMF species in our model system, a corresponding change in the expression of mycorrhiza-inducible Pht1 transporters was only marginally detected. Besides Pi uptake across the plant's periarbuscular membrane, the release of Pi from AMF into the periarbuscular space is another crucial step of mycorrhizal Pi pathway.…”

“…Nevertheless, its expression was strongly reduced in roots of sorghum cultivated in mixed culture with flax. In this treatment, the mycorrhizal Pi acquisition of sorghum was much lower compared to the other treatments (for details see 3,4 ). Additionally, RiPT5 was the only fungal transporter exhibiting a positive correlation with mycorrhizal Pi acquisition of sorghum ( Fig.…”

“…A similar correlation between mycorrhizal Pi acquisition and expression of FmPT5 in sorghum roots could strengthen the importance of these homologous transporters for the intraradical mycorrhizal Pi transfer from AMF to plants. However, expression of RiPT5 was not affected in flax roots, although flax increased its mycorrhizal Pi acquisition twofold from mono-to mixed culture (for details see 3,4 ). Similarly, expression of fungal Pi transporters was generally more related to mycorrhizal Pi acquisition of sorghum compared to flax (Table S3).…”

“…3 More recently, we tried to shed light on the different abilities of flax and sorghum to acquire nutrients from CMNs depending on the identity of the fungal symbiont by focusing on the model plant's phosphate acquisition pathways. 4 Plants associated with AMF exhibit a specific symbiotic phosphate uptake pathway, which begins at the extraradical hyphae in the soil, from where inorganic phosphate (Pi) is translocated toward the roots and released from the arbuscule into the periarbuscular space. 5 There, it is taken up across the plant's periarbuscular membrane by specifically induced phosphate transporters belonging to the Pht1 family of plant Pi transporter.…”

“…However, mechanisms of Pi release from fungus to the periarbuscular space are less-well studied and remain obscure up to now. 5 In order to reveal the role of fungal Pi transporter in mycorrhizal Pi pathway, expression of several fungal Pi transporters genes of Rhizophagus irregularis (strain TERI commercial) and Funeliformis mosseae (strain ISCB 22, both kept in our fungal strain collection 9 ) were investigated in roots of flax and sorghum of the model system used in previously published studies 3,4 (Table S1 and S2). We designed gene expression assays for different Pi transporters of F. mosseae (FmPT1, FmPT3, FmPT7) and R. irregularis (RiPT1, RiPT3, RiPT5, RiPT7).…”