Functional analysis of the novel mycorrhiza‐specific phosphate transporter A s PT 1 and PHT 1 family from A stragalus sinicus during the arbuscular mycorrhizal symbiosis

Summary Arbuscular mycorrhizas contribute significantly to inorganic phosphate ( P i) uptake in plants. Gene networks involved in the regulation and function of the P ht1 family transporters in legume species during AM symbiosis are not fully understood. In order to characterize the six distinct members of P ht1 transporters in mycorrhizal A stragalus sinicus , we combined cellular localization, heterologous functional expression in yeast with expression/subcellular localization studies and reverse genetics approaches in planta. P ht1;1 and P ht1;4 silenced lines were generated to uncover the role of the newly discovered dependence of the AM symbiosis on another phosphate transporter A s PT 1 besides A s PT 4. These P ht1 transporters are triggered in P i‐starved mycorrhizal roots. A s PT 1 and A s PT 4 were localized in arbuscule‐containing cells of the cortex. The analysis of promoter sequences revealed conserved motifs in both A s PT 1 and A s PT 4 . A s PT 1 overexpression showed higher mycorrhization levels than controls for parameters analysed, including abundance of arbuscules. By contrast, knockdown of A s PT 1 by RNA interference led to degenerating or dead arbuscule phenotypes identical to that of A s PT 4 silencing lines. A s PT 4 but not A s PT 1 is required for symbiotic P i uptake. These results suggest that both, A s PT 1 and A s PT 4, are required for the AM symbiosis, most importantly, A s PT 1 may serve as a novel symbiotic transporter for AM development.