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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 ofMtHEXO2during symbiosis.We found that expression ofMtHEXO2is associated with AM symbiosis and nodulation.MtHEXO2expression in the rhizodermis was upregulated in response to applied chitotetraose, chitoheptaose, and LCOs.M. truncatulamutants 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).Hexo2mutants exhibited reduced colonization by AM fungi; however, nodulation was not affected inhexo2mutants.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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Nodule‐specific Cu + ‐chaperone NCC1 is required for symbiotic nitrogen fixation in Medicago truncatula root nodules
Summary Cu+‐chaperones are a diverse group of proteins that allocate Cu+ions to specific copper proteins, creating different copper pools targeted to specific physiological processes.Symbiotic nitrogen fixation carried out in legume root nodules indirectly requires relatively large amounts of copper, for example for energy delivery via respiration, for which targeted copper deliver systems would be required.MtNCC1 is a nodule‐specific Cu+‐chaperone encoded in theMedicago truncatulagenome, with a N‐terminus Atx1‐like domain that can bind Cu+with picomolar affinities. MtNCC1 is able to interact with nodule‐specific Cu+‐importer MtCOPT1.MtNCC1is expressed primarily from the late infection zone to the early fixation zone and is located in the cytosol, associated with plasma and symbiosome membranes, and within nuclei. Consistent with its key role in nitrogen fixation,ncc1mutants have a severe reduction in nitrogenase activity and a 50% reduction in copper‐dependent cytochromecoxidase activity.A subset of the copper proteome is also affected in thencc1mutant nodules. Many of these proteins can be pulled down when using a Cu+‐loaded N‐terminal MtNCC1 moiety as a bait, indicating a role in nodule copper homeostasis and in copper‐dependent physiological processes. Overall, these data suggest a pleiotropic role of MtNCC1 in copper delivery for symbiotic nitrogen fixation.
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- Award ID(s):
- 2233714
- PAR ID:
- 10472400
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- New Phytologist
- Volume:
- 241
- Issue:
- 2
- ISSN:
- 0028-646X
- Format(s):
- Medium: X Size: p. 793-810
- Size(s):
- p. 793-810
- Sponsoring Org:
- National Science Foundation
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