Ectomycorrhizal symbiosis enhances tolerance to low phosphorous through expression of phosphate transporter genes in masson pine (Pinus massoniana)

Abstract

Ectomycorrhizal symbiosis promotes the growth of masson pine (Pinus massoniana) in low-phosphorus (low-P) conditions; however, the mechanism underlying this phenomenon has not yet been fully described. Here, we cloned four members of the Pht1 phosphate transporter protein family (GenBank accession: AMR43649.1 to AMR43652.1) encoding phosphate transporters in masson pine (PmPTs) by rapid amplification of cDNA ends (RACE) and characterized them in Boletus edulis and Pisolithus tinctorius colonized plants under low-P stress. PmPT1 to PmPT4 encoded 548, 548, 535, 535 amino acid polypeptides, respectively, containing the typical domain of the Pi:H+ symporter (PHS-transporter). Homology multiple sequence alignment indicated that these PmPTs were highly similar to phosphate transporters from other species. The polypeptides were characterized by high hydropathicity and contained 12 putative intra-membrane regions and 1 cytoplasmic loop. The temporal and spatial expression profiles showed higher expression of these PmPTs in ectomycorrhiza (ECM)-inoculated plants compared to non-inoculated ones. In addition, expressions of these PmPT members shared a similar pattern and might be intensively activated by low-P stress or inhibited under P excess. Interestingly, the ECM-colonized plants accumulated more phosphate compared to non-ECM-colonized specimens when exposed to low-P. Therefore, enhanced low-P tolerance in ECM-inoculated masson pine to low-P stress was at least partially dependent on the up-regulation of phosphate transporter genes, reflecting that the intimate interaction between plants and ECM fungi resulted in the improvement of P nutrition.