Rhizobial lipochitooligosaccharidic Nod factors (NFs), specified by We examined the nodulation ability of We show that the Our findings reveal that a newly evolved gene in R108,
This content will become publicly available on June 1, 2025
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 We biochemically characterized five flavonoid‐ 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 ( We conclude that: the loss of ChOMT1 greatly reduces root DHMC levels; ChOMT1 or OMT2 are important for
- Award ID(s):
- 2233714
- PAR ID:
- 10507437
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- New Phytologist
- Volume:
- 242
- Issue:
- 5
- ISSN:
- 0028-646X
- Page Range / eLocation ID:
- 2195 to 2206
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Summary nod genes, are the primary determinants of host specificity in the legume–Rhizobia symbiosis.Medicago truncatula cv Jemalong A17 andM. truncatula ssp.tricycla R108 with theSinorhizobium meliloti nodF/nodL mutant, which produces modified NFs. We then applied genetic and functional approaches to study the genetic basis and mechanism of nodulation of R108 by this mutant.nodF/nodL mutant can nodulate R108 but not A17. Using genomics and reverse genetics, we identified a newly evolved, chimeric LysM receptor‐like kinase gene in R108,LYK2bis , which is responsible for the phenotype and can allow A17 to gain nodulation with thenodF/nodL mutant. We found thatLYK2bis is involved in nodulation by mutants producing nonO ‐acetylated NFs and interacts with the key receptor protein NFP. Many, but not all, naturalS. meliloti andS. medicae strains tested requireLYK2bis for efficient nodulation of R108.LYK2bis , extends nodulation specificity to mutants producing nonO ‐acetylated NFs and is important for nodulation by many naturalSinorhizobia . Evolution of this gene may present an adaptive advantage to allow nodulation by a greater variety of strains. -
Summary Establishment of symbiosis between plants and arbuscular mycorrhizal (AM) fungi depends on fungal chitooligosaccharides (COs) and lipo‐chitooligosaccharides (LCOs). The latter are also produced by nitrogen‐fixing rhizobia to induce nodules on leguminous roots. However, host enzymes regulating structure and levels of these signals remain largely unknown.
Here, we analyzed the expression of a β‐
N ‐acetylhexosaminidase gene ofMedicago truncatula (MtHEXO2 ) and biochemically characterized the enzyme. Mutant analysis was performed to study the role ofMtHEXO2 during symbiosis.We found that expression of
MtHEXO2 is associated with AM symbiosis and nodulation.MtHEXO2 expression in the rhizodermis was upregulated in response to applied chitotetraose, chitoheptaose, and LCOs.M. truncatula mutants deficient in symbiotic signaling did not show induction ofMtHEXO2 . Subcellular localization analysis indicated that MtHEXO2 is an extracellular protein. Biochemical analysis showed that recombinant MtHEXO2 does not cleave LCOs but can degrade COs intoN ‐acetylglucosamine (GlcNAc).Hexo2 mutants exhibited reduced colonization by AM fungi; however, nodulation was not affected inhexo2 mutants.In conclusion, we identified an enzyme, which inactivates COs and promotes the AM symbiosis. We hypothesize that GlcNAc produced by MtHEXO2 may function as a secondary symbiotic signal.
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Nod factors secreted by nitrogen-fixing rhizobia are lipo-chitooligosaccharidic signals required for establishment of the nodule symbiosis with legumes. In
Medicago truncatula , the Nod factor hydrolase 1 (MtNFH1) was found to cleave Nod factors ofSinorhizobium meliloti . Here, we report that the class V chitinase MtCHIT5b ofM. truncatula expressed inEscherichia coli can release lipodisaccharides from Nod factors. Analysis ofM. truncatula mutant plants indicated that MtCHIT5b, together with MtNFH1, degradesS. meliloti Nod factors in the rhizosphere.MtCHIT5b expression was induced by treatment of roots with purified Nod factors or inoculation with rhizobia. MtCHIT5b with a fluorescent tag was detected in the infection pocket of root hairs. Nodulation of aMtCHIT5b knockout mutant was not significantly altered whereas overexpression ofMtCHIT5b resulted in fewer nodules. Reduced nodulation was observed whenMtCHIT5b andMtNFH1 were simultaneously silenced in RNA interference experiments. Overall, this study shows that nodule formation ofM. truncatula is regulated by a second Nod factor cleaving hydrolase in addition to MtNFH1. -
Summary Symbiotic nitrogen fixation in legumes is mediated by an interplay of signaling processes between plant hosts and rhizobial symbionts. In legumes, several secreted protein families have undergone expansions and play key roles in nodulation. Thus, identifying lineage‐specific expansions (
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