Symbioses: Plant, Animal, and Microbe Interactions
Schilling, Cory , De Carvalho, Peter , Guinel, Frederique .
Approach-grafting with mutants R50 (sym16) and E151 (sym15) to study autoregulation of nodulation in pea (Pisum sativum L).
Pisum sativum develops a mutualistic relationship with the soil-borne bacterium Rhizobium leguminosarum resulting in the development of a nitrogen-fixing nodule. This symbiosis is regulated by environmental and hormonal cues, and a systemic process known as autoregulation of nodulation (AON), which results in the inhibition of nodule development. In short, inoculated roots synthesize a compound which ascends to the shoot; its perception there leads to the production of a molecule which, translocated to the root, inhibits nodule formation on younger roots. To better understand the signalling pathway of AON in pea, an approach-grafting technique has previously been developed and carried out on mutants, the nodulation phenotype of which is root-controlled. Here, we performed this technique on two low-nodulating mutants R50 and E151, both known to be root-controlled, to study whether they are defective in AON and if so to determine the location of their defects. The technique allows root systems to be kept isolated so that one root known as sensor can be inoculated earlier than the other root known as receptor. The delay in inoculation allows one to see the effects of the sensor inoculation onto the receptor nodulation. Two types of grafting were achieved: isografts which involve the grafting of two individuals of the same pea line and heterografts which are made between one of the mutants and its wild-type Sparkle (WT). The isografts were first compared to non-grafted individuals having been subjected to the same experimental conditions to assess the effects of grafting on nodule numbers. Interestingly, whereas grafting affected neither WT nor R50, it increased nodulation on E151. The isografts were later compared to the heterografts; we compared the sensor from the WT (sensor)/ mutant (receptor) graft and the receptor from the mutant/WT graft to those of the WT isograft. In R50 we observed significant increases in WT nodulation, whereas in E151 no significant differences were seen. Previous work links AON strength with the location of the mutant defect, i.e., a mutant affected early in the nodulation transduction pathway has a weaker inhibitory effect on the WT receptor than a mutant affected later. With this in mind, we conclude that the R50 defect is located ahead of the E151 defect. This matches the results of the developmental studies of these two mutants. We propose that it is the initiation of the periclinal divisions in the inner cortex which triggers the production of the AON root signal.
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1 - Wilfrid Laurier University, Department of Biology, 70, University Avenue West, Waterloo, On, N2L 3C5, Canada
2 - Wilfrid Laurier University, Biology, 70, University Avenue W, Waterloo, Ontario, N2L 3C5, Canada
3 - Wilfrid Laurier University, Biology, 75 University Avenue W, Waterloo, ON, N2L 3C5, Canada
Autoregulation of nodulation
Presentation Type: Poster:Posters for Topics
Location: Battelle South/Convention Center
Date: Monday, July 9th, 2012
Time: 5:30 PM