The down-regulation of Mt4-like genes by phosphate fertilization occurs systemically and involves phosphate translocation to the shoots.
Mt4 is a cDNA representing a phosphate-starvation-inducible gene from Medicago truncatula that is down-regulated in roots in response to inorganic phosphate (Pi) fertilization and colonization by arbuscular mycorrhizal fungi. Split-root experiments revealed that the expression of the Mt4 gene in M. truncatula roots is down-regulated systemically by both Pi fertilization and colonization by arbuscular mycorrhizal fungi. A comparison of Pi levels in these tissues suggested that this systemic down-regulation is not caused by Pi accumulation. Using a 30-bp region of the Mt4 gene as a probe, Pi-starvation-inducible Mt4-like genes were detected in Arabidopsis and soybean (Glycine max L.), but not in corn (Zea mays L.). Analysis of the expression of the Mt4-like Arabidopsis gene, At4, in wild-type Arabidopsis and pho1, a mutant unable to load Pi into the xylem, suggests that Pi must first be translocated to the shoot for down-regulation to occur. The data from the pho1 and split-root studies are consistent with the presence of a translocatable shoot factor responsible for mediating the systemic down-regulation of Mt4-like genes in roots.
Burleigh
S H
SH
The Samuel Roberts Noble Foundation, Plant Biology Division, 2510 Sam Noble Parkway, Ardmore, Oklahoma 73402, USA.
Harrison
M J
MJ
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics; D001483:Base Sequence; D018076:DNA, Complementary / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D015536:Down-Regulation / Q000187:drug effects; D005658:Fungi / Q000472:pathogenicity; D017343:Genes, Plant; D000455:Medicago sativa / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D010710:Phosphates / Q000378:metabolism / Q000494:pharmacology; D010940:Plant Proteins / Q000235:genetics*; D018520:Plant Shoots / Q000378:metabolism; D012689:Sequence Homology, Nucleic Acid; D013025:Glycine max / Q000235:genetics
D018076:DNA, Complementary; D018744:DNA, Plant; C114548:Mt4 protein, Medicago truncatula; D010710:Phosphates; D010940:Plant Proteins