Feedback regulation of the Bradyrhizobium japonicum nodulation genes.
Lipochitin Nod signals are produced by rhizobia and are required for the establishment of a nitrogen-fixing symbiosis with a legume host. The nodulation genes encode products required for the synthesis of this signal and are induced in response to plant-produced flavonoid compounds. The addition of chitin and lipo-chitin oligomers to Bradyrhizobium japonicum cultures resulted in a significant reduction in the expression of a nod-lacZ fusion. Intracellular expression of NodC, encoding a chitin synthase, also reduced nod gene expression. In contrast, expression of the ChiB chitinase increased nod gene expression. The chain length of the oligosaccharide was important in feedback regulation, with chitotetraose molecules the best modulators of nod gene expression. Feedback regulation is mediated by the induction of nolA by chitin, resulting in elevated levels of the repressor protein, NodD2.
Loh
J T
JT
Center for Legume Research, Department of Microbiology, The University of Tennessee, Knoxville, TN 37996, USA.
Stacey
G
G
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D020369:Bradyrhizobium / Q000235:genetics* / Q000378:metabolism; D002686:Chitin / Q000378:metabolism; D002687:Chitin Synthase / Q000235:genetics / Q000378:metabolism; D002688:Chitinases / Q000235:genetics / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D007887:Fabaceae / Q000382:microbiology; D005246:Feedback; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D008070:Lipopolysaccharides / Q000737:chemistry / Q000378:metabolism; D008954:Models, Biological; D017351:N-Acetylglucosaminyltransferases / Q000235:genetics / Q000378:metabolism; D009586:Nitrogen Fixation / Q000235:genetics; D009844:Oligosaccharides / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D013559:Symbiosis
D001426:Bacterial Proteins; D017931:DNA Primers; D008070:Lipopolysaccharides; C060773:NodD protein, Bacteria; D009844:Oligosaccharides; D010940:Plant Proteins; C023023:lipid-linked oligosaccharides; D002686:Chitin; C012238:chitotetrose; D017351:N-Acetylglucosaminyltransferases; C060771:NodC protein, Rhizobiales; D002687:Chitin Synthase; D002688:Chitinases; C094255:PLC-B protein, Phytolacca americana