Identification of two conserved cis-acting elements, MYCS and P1BS, involved in the regulation of mycorrhiza-activated phosphate transporters in eudicot species

In this study, six putative promoter regions of phosphate transporter Pht1; 3, Pht1; 4 and Pht1; 5 genes were isolated from eggplant and tobacco using the inverse polymerase chain reaction (iPCR). The isolated sequences show evolutionary conservation and divergence within/between the two groups of Pht1; 3 and Pht1; 4/Pht1; 5. Histochemical analyses showed that all six promoter fragments were sufficient to drive beta-glucuronidase (GUS) expression specifically in arbuscular mycorrhizal (AM) tobacco roots and were confined to distinct cells containing AM fungal structures (arbuscules or intracellular hyphae). A series of promoter truncation and mutation analyses combined with phylogenetic footprinting of these promoters revealed that at least two cis-regulatory elements - the mycorrhiza transcription factor binding sequence (MYCS) first identified in this study and P1BS - mediated the transcriptional activation of the AM-mediated inorganic phosphate (Pi) transporter genes. Deletion or partial mutation of either of the two motifs in the promoters could cause a remarkable decrease, or even complete absence, of the promoter activity. Our results propose that uptake of inorganic phosphate (Pi) by AM fungi is regulated, at least partially, in an MYCS- and P1BS-dependent manner in eudicot species. Our finding offers new insights into the molecular mechanisms underlying the coordination between the AM and the Pi signalling pathways.