Structure-function analysis of nod factor-induced root hair calcium spiking in Rhizobium-legume symbiosis.
In the Rhizobium-legume symbiosis, compatible bacteria and host plants interact through an exchange of signals: Host compounds promote the expression of bacterial biosynthetic nod (nodulation) genes leading to the production of a lipochito-oligosaccharide signal, the Nod factor (NF). The particular array of nod genes carried by a given species of Rhizobium determines the NF structure synthesized and defines the range of legume hosts by which the bacterium is recognized. Purified NF can induce early host responses even in the absence of live Rhizobium One of the earliest known host responses to NF is an oscillatory behavior of cytoplasmic calcium, or calcium spiking, in root hair cells, initially observed in Medicago spp. and subsequently characterized in four other genera (D.W. Ehrhardt, R. Wais, S.R. Long [1996] Cell 85: 673-681; S.A. Walker, V. Viprey, J.A. Downie [2000] Proc Natl Acad Sci USA 97: 13413-13418; D.W. Ehrhardt, J.A. Downie, J. Harris, R.J. Wais, and S.R. Long, unpublished data). We sought to determine whether live Rhizobium trigger a rapid calcium spiking response and whether this response is NF dependent. We show that, in the Sinorhizobium meliloti-Medicago truncatula interaction, bacteria elicit a calcium spiking response that is indistinguishable from the response to purified NF. We determine that calcium spiking is a nod gene-dependent host response. Studies of calcium spiking in M. truncatula and alfalfa (Medicago sativa) also uncovered the possibility of differences in early NF signal transduction. We further demonstrate the sufficiency of the nod genes for inducing calcium spiking by using Escherichia coli BL21 (DE3) engineered to express 11 S. meliloti nod genes.
Wais
Rebecca J
RJ
Department of Biological Sciences, Howard Hughes Medical Institute, Stanford University, CA 94305, USA.
Keating
David H
DH
Long
Sharon R
SR
D000123:Acetyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000217:Acyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000581:Amidohydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002240:Carbohydrate Sequence; D004926:Escherichia coli / Q000235:genetics; D008070:Lipopolysaccharides / Q000494:pharmacology; D029902:Medicago / Q000235:genetics / Q000254:growth & development / Q000382:microbiology*; D008969:Molecular Sequence Data; D017351:N-Acetylglucosaminyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development / Q000382:microbiology*; D021281:Quantitative Structure-Activity Relationship; D016961:Rhizobium leguminosarum / Q000254:growth & development*; D016962:Sinorhizobium meliloti / Q000254:growth & development*; D013430:Sulfate Adenylyltransferase; D015238:Sulfotransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013559:Symbiosis
D001426:Bacterial Proteins; D008070:Lipopolysaccharides; C092082:Nod factor IV, Rhizobium meliloti; C068605:nodF protein, Rhizobium; C075085:nodP protein, Rhizobium; C073606:nodB protein, Bacteria; D000217:Acyltransferases; D000123:Acetyltransferases; C060770:NodA protein, Rhizobiales; D017351:N-Acetylglucosaminyltransferases; C060771:NodC protein, Rhizobiales; D013430:Sulfate Adenylyltransferase; C092976:NodH protein, Sinorhizobium meliloti; D015238:Sulfotransferases; D000581:Amidohydrolases; D002118:Calcium