Abstract
Legume nodulation requires the detection of flavonoids in the rhizosphere by rhizobia to activate their production of Nod factor countersignals. Here we investigated the flavonoids involved in nodulation of Medicago truncatula. We biochemically characterized five flavonoid-O-methyltransferases (OMTs) and a lux-based nod gene reporter was used to investigate the response of Sinorhizobium medicae NodD1 to various flavonoids. We found that chalcone-OMT 1 (ChOMT1) and ChOMT3, but not OMT2, 4, and 5, were able to produce 4,4'-dihydroxy-2'-methoxychalcone (DHMC). The bioreporter responded most strongly to DHMC, while isoflavones important for nodulation of soybean (Glycine max) showed no activity. Mutant analysis revealed that loss of ChOMT1 strongly reduced DHMC levels. Furthermore, chomt1 and omt2 showed strongly reduced bioreporter luminescence in their rhizospheres. In addition, loss of both ChOMT1 and ChOMT3 reduced nodulation, and this phenotype was strengthened by the further loss of OMT2. We conclude that: the loss of ChOMT1 greatly reduces root DHMC levels; ChOMT1 or OMT2 are important for nod gene activation in the rhizosphere; and ChOMT1/3 and OMT2 promote nodulation. Our findings suggest a degree of exclusivity in the flavonoids used for nodulation in M. truncatula compared to soybean, supporting a role for flavonoids in rhizobial host range.
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Claims 10
Claim · model-written summary
ChOMT1 and ChOMT3 produced DHMC.
- Taxon
- Medicago truncatula
Medicago truncatulae1 - Gene
- ChOMT1 and ChOMT3e2
- Outcome
- produce 4,4'-dihydroxy-2'-methoxychalcone (DHMC)e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“chalcone-OMT 1 (ChOMT1) and ChOMT3, but not OMT2, 4, and 5, were able to produce 4,4'-dihydroxy-2'-methoxychalcone (DHMC)”
e1“nodulation of Medicago truncatula”
e2“loss of both ChOMT1 and ChOMT3 reduced nodulation”
Claim · model-written summary
OMT2, OMT4 and OMT5 did not produce DHMC.
- Taxon
- Medicago truncatulaMedicago truncatulae1
- Gene
- OMT2, 4, and 5e0
- Outcome
- produce 4,4'-dihydroxy-2'-methoxychalcone (DHMC)e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“but not OMT2, 4, and 5, were able to produce 4,4'-dihydroxy-2'-methoxychalcone (DHMC)”
e1“nodulation of Medicago truncatula”
Claim · model-written summary
The Sinorhizobium medicae NodD1 bioreporter responded most strongly to DHMC.
- Taxon
- Medicago truncatulaMedicago truncatulae2
- Interactor
- Sinorhizobium medicae
Sinorhizobium medicaee1symbiont - Compound
- DHMCe0
- Outcome
- bioreporter respondede0
- Direction
- most stronglye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The bioreporter responded most strongly to DHMC”
e1“Sinorhizobium medicae NodD1”
e2“nodulation of Medicago truncatula”
Claim · model-written summary
Soybean-associated isoflavones showed no bioreporter activity.
- Taxon
- Glycine max
Glycine maxe0 - Interactor
- Sinorhizobium medicaeSinorhizobium medicaee1symbiont
- Compound
- isoflavonese0
- Outcome
- activitye0
- Direction
- no activitye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“isoflavones important for nodulation of soybean (Glycine max) showed no activity”
e1“Sinorhizobium medicae NodD1”
Claim · model-written summary
Loss of ChOMT1 strongly reduced DHMC levels.
- Taxon
- Medicago truncatulaMedicago truncatulae1
- Treatment
- loss of ChOMT1e0
- Gene
- ChOMT1e0
- Outcome
- DHMC levelse0
- Direction
- strongly reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“loss of ChOMT1 strongly reduced DHMC levels”
e1“nodulation of Medicago truncatula”
Claim · model-written summary
The chomt1 mutant had strongly reduced rhizosphere bioreporter luminescence.
- Taxon
- Medicago truncatulaMedicago truncatulae1
- Material
- chomt1e0
- Treatment
- chomt1e0
- Interactor
- Sinorhizobium medicaeSinorhizobium medicaee2symbiont
- Outcome
- bioreporter luminescencee0
- Direction
- strongly reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“chomt1 and omt2 showed strongly reduced bioreporter luminescence in their rhizospheres”
e1“nodulation of Medicago truncatula”
e2“Sinorhizobium medicae NodD1”
Claim · model-written summary
The omt2 mutant had strongly reduced rhizosphere bioreporter luminescence.
- Taxon
- Medicago truncatulaMedicago truncatulae1
- Material
- omt2e0
- Treatment
- omt2e0
- Interactor
- Sinorhizobium medicaeSinorhizobium medicaee2symbiont
- Outcome
- bioreporter luminescencee0
- Direction
- strongly reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“chomt1 and omt2 showed strongly reduced bioreporter luminescence in their rhizospheres”
e1“nodulation of Medicago truncatula”
e2“Sinorhizobium medicae NodD1”
Claim · model-written summary
Combined loss of ChOMT1 and ChOMT3 reduced nodulation.
- Taxon
- Medicago truncatulaMedicago truncatulae1
- Treatment
- loss of both ChOMT1 and ChOMT3e0
- Gene
- ChOMT1 and ChOMT3e0
- Outcome
- nodulatione0
- Direction
- reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“loss of both ChOMT1 and ChOMT3 reduced nodulation”
e1“nodulation of Medicago truncatula”
Claim · model-written summary
Additional loss of OMT2 strengthened the reduced nodulation phenotype.
- Taxon
- Medicago truncatulaMedicago truncatulae2
- Treatment
- further loss of OMT2e0
- Gene
- OMT2e0
- Outcome
- nodulatione1
- Direction
- strengthenede0
- Comparator
- loss of both ChOMT1 and ChOMT3e1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“this phenotype was strengthened by the further loss of OMT2”
e1“loss of both ChOMT1 and ChOMT3 reduced nodulation”
e2“nodulation of Medicago truncatula”
Claim · model-written summary
The authors infer flavonoid use for nodulation differs between M. truncatula and soybean and may shape rhizobial host range.
- Taxon
- M. truncatulaMedicago truncatulae0
- Compound
- flavonoidse0
- Outcome
- rhizobial host rangee0
- Qualifier
- degree of exclusivitye0
- Comparator
- soybeane0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Our findings suggest a degree of exclusivity in the flavonoids used for nodulation in M. truncatula compared to soybean, supporting a role for flavonoids in rhizobial host range.”