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

International audienceGene networks involved in Pi acquisition and homeostasis in woody perennial species able to form mycorrhizal symbioses are poorly known. Here, we describe the features of the 12 genes coding for inorganic phosphate (Pi) transporters of the Pht1 family in Populus trichocarpa Torr. & A.Gray ex Hook. Individual Pht1 transporters play distinct roles in acquiring and translocating Pi in different tissues of mycorrhizal and nonmycorrhizal poplar during different growth conditions and developmental stages. Pi starvation triggered the up-regulation of most members of the Pht1 family; especially PtPT9 and PtPT11. PtPT9 and PtPT12 showed a striking up-regulation in ecto- and endomycorrhizas, whereas PtPT1 and PtPT11 were strongly down regulated. PtPT10 transcripts were highly abundant in AM roots only. PtPT8 and PtPT10 are phylogenetically associated to the arbuscular mycorrhiza (AM)-inducible Pht1 sub-family I. The analysis of promoter sequences revealed conserved motifs similar to other AM inducible orthologs in PtPT10 only. To gain more insight into gene regulatory mechanisms governing the AM symbiosis in woody plant species, the activation of the poplar PtPT10 promoter was investigated and detected in AM of Solanum tuberosum roots. These results indicated that the regulation of AM-inducible Pi transporter genes is conserved between perennial woody and herbaceous plant species. Moreover, poplar has developed an alternative Pi uptake pathway distinct from AM plants allowing ectomycorrhizal poplar to recruit PtPT9 and PtPT12 to cope with limiting Pi concentrations in forest soils