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

Abstract

Summary• 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 b-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.

How does phosphate status influence the development of the arbuscular mycorrhizal symbiosis?

“…2,14 It is well known that Pi level is negatively correlated with AM development, and that the inhibition of high Pi supply to AM development is more likely driven by the host plants, but not the fungi. [11][12][13][14]18 While the knowledge about whether the inhibition by high Pi supply happens at a certain stage or multiple stages signaling molecules other than strigolactones or high Pi affects the symbiosis at other stage(s).…”

“…Key words: phosphate, arbuscular mycorrhiza, symbiosis, signaling, cross-talk, phytohormone the molecular mechanisms responsible for the inhibition of AM development by high level Pi supply. [11][12][13] In this mini-review, we summarized the current understanding for the molecular mechanisms of Pi as repressor for the AMF symbiosis development, which is still largely unknown and needs substantial further investigations.…”

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

“…6A). This motif was shown to be highly conserved in AM-inducible Pht1 genes in dicots (Karandashov et al, 2004;Chen et al, 2011) but was never described in trees and especially in Malphigiales, to which poplar belongs.…”

“…6A). Interestingly, the function of and cooperativity between the two motifs have recently been investigated in tobacco (Chen et al, 2011). The function of the CTTC, P1BS, and other motifs of still unknown function in the regulation of AM-or EM-inducible Pht1 genes in poplar remains to be elucidated.…”

TheLotus japonicus MAMIgene links root development, arbuscular mycorrhizal symbiosis and phosphate availability

“…Both the P1BS and the MYCS motifs have been shown to be necessary for the proper induction of AM responsive Pi transporters. 8 Coherently with this hypothesis, the same motifs are also present in the promoter of LjPT3, another Pi-transporter induced by the AM symbiosis, 9 even if the distance between the two sequences is far more pronounced than usually observed. LjPT1 and LjPT2 are other two genes which are involved in Pi transport but are not induced by AM symbiosis.…”