Long-distance translocation of phosphate in arbuscular mycorrhizal association

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Polyphosphate synthetic activity and phosphatase specific to mycorrhizal formation were investigated to clarify the mechanism of phosphorus (P) acquisition in arbuscular mycorrhizal association.1. Polyphosphate synthesis in arbuscular mycorrhizal fungiPolyphosphate (polyP) is a linear polymer of phosphate linked by high-energy bonds and plays significant roles in P-delivery in the associations. Extraradical hyphae were collected and subjected to cell fractionation to isolated organelles involved in polyP synthesis. PolyP synthetic activity was detected and characterized for the first time in fungi. PolyP was synthesized using ATP as substrate, but the synthesis was not supported by proton-gradients created by H^+-ATPase. The activity was induced in the P-deficient hyphae by phosphate application.2. Up-regulation of secreted acid phosphatase gene in host plantThe mycorrhiza-responsive phosphatase was detected by electrophoresis, purified by column chromatography and characterized as aci … More d phosphatase that was secreted into rhizosphere. A cDNA fragment of the phosphatase gene (TpPAPI) was amplified by degenerate primers designed based on the N-terminal amino acid sequence. The full-length cDNA was obtained by the RACE technique. TpPAPI was of host origin, and the cDNA was 1,843 bp long with a predicted open reading frame of polypeptide of 466 amino acids. Phylogenetic analysis revealed that the gene fell into the cluster of plant high molecular weight purple acid phosphatase. Expression analysis of the TpPAPI showed that the levels of transcripts increased 8-fold by mycorrhizal colonization. Western blot analysis revealed that the 57 kDa protein corresponding to the mycorrhiza-responsive phosphatase increased by mycorrhizal colonization. The present study proposes a new strategy for acquisition of P in arbuscular mycorrhizal associations in which the fungal partner activates a part of the low-P adaptation system of the plant partner, phosphatase secretion, and improves the overall efficiency of P uptake. Less