Abstract
Three major components of lipopolysaccharide in rhizobia, namely core polysaccharide, o-antigen, and lipid A, often act as microbe-associated molecular patterns to participate in the symbiosis between rhizobia and legumes. Rhizobia have a different lipid A structure from other gram-negative bacteria. The 3-hydroxy group on the 2′ or 3′ myristate acyl chain of its lipid A is substituted by a unique very-long-chain fatty acid (VLCFA), 27-hydroxyoctacosanoic acid. VLCFAs are usually transferred to lipid A by an acyltransferase, MsbB. In this research, we constructed an msbB deletion mutant and complementary and overexpression strains of Sinorhizobium fredii HH103 and investigated their free-living and symbiotic phenotypes. The findings revealed that deletion of msbB had no impact on the autonomous growth of HH103 yet significantly reduced the resistance of rhizobia to abiotic stresses. Promoter-GUS assays revealed that msbB was mainly expressed at the early stage of nodulation. Quantitative analysis of early infection events revealed that the mutation of msbB significantly reduced root hair curling, infection threads, and nodule primordia, suggesting impairment of the symbiotic infection process. Nodulation assay and transmission electron microscopy analysis of the nodule ultrastructure further showed that msbB deletion led to the formation of small and ineffective root nodules without colonization of rhizobia, thereby causing a loss of nitrogen fixation capacity. RNA-seq analysis indicated that HH103Ω msbB inoculation may impair early symbiotic signaling and trigger a localized defense response in the soybean root to result in symbiotic deficiencies. Taken together, these results reveal the important role of VLCFAs in soybean rhizobia in the establishment of effective symbiosis and nodule nitrogen fixation. [Formula: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .
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Claims 10
Claim · model-written summary
Deleting msbB did not alter autonomous growth of rhizobia.
- Taxon
- Soybean
Glycine maxt0 - Treatment
- deletion of msbBe0
- Interactor
- HH103e0symbiont
- Gene
- msbBe0
- Outcome
- autonomous growth of HH103e0
- Direction
- no impacte0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“deletion of msbB had no impact on the autonomous growth of HH103”
t0“Soybean”
Claim · model-written summary
Deleting msbB reduced rhizobial resistance to abiotic stresses.
- Taxon
- SoybeanGlycine maxt0
- Treatment
- deletion of msbBe0
- Interactor
- rhizobiae0symbiont
- Gene
- msbBe0
- Outcome
- resistance of rhizobia to abiotic stressese0
- Direction
- reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“deletion of msbB had no impact on the autonomous growth of HH103 yet significantly reduced the resistance of rhizobia to abiotic stresses”
t0“Soybean”
Claim · model-written summary
msbB expression was mainly at the early nodulation stage.
- Taxon
- SoybeanGlycine maxt0
- Organ / stage
- early stage of nodulatione0
- Gene
- msbBe0
- Outcome
- mainly expressed at the early stage of nodulatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“msbB was mainly expressed at the early stage of nodulation”
t0“Soybean”
Claim · model-written summary
msbB mutation significantly reduced root hair curling.
- Taxon
- SoybeanGlycine maxt0
- Treatment
- mutation of msbBe0
- Gene
- msbBe0
- Outcome
- root hair curlinge0
- Direction
- reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“mutation of msbB significantly reduced root hair curling, infection threads, and nodule primordia”
t0“Soybean”
Claim · model-written summary
msbB mutation significantly reduced infection threads.
- Taxon
- SoybeanGlycine maxt0
- Treatment
- mutation of msbBe0
- Gene
- msbBe0
- Outcome
- infection threadse0
- Direction
- reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“mutation of msbB significantly reduced root hair curling, infection threads, and nodule primordia”
t0“Soybean”
Claim · model-written summary
msbB mutation significantly reduced nodule primordia.
- Taxon
- SoybeanGlycine maxt0
- Treatment
- mutation of msbBe0
- Gene
- msbBe0
- Outcome
- nodule primordiae0
- Direction
- reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“mutation of msbB significantly reduced root hair curling, infection threads, and nodule primordia”
t0“Soybean”
Claim · model-written summary
msbB deletion led to small and ineffective root nodules without rhizobial colonization.
- Taxon
- SoybeanGlycine maxt0
- Organ / stage
- root nodulese0
- Treatment
- msbB deletione0
- Interactor
- rhizobiae0symbiont
- Gene
- msbBe0
- Outcome
- small and ineffective root nodules without colonization of rhizobiae0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“msbB deletion led to the formation of small and ineffective root nodules without colonization of rhizobia”
t0“Soybean”
Claim · model-written summary
msbB deletion caused loss of nitrogen fixation capacity.
- Taxon
- SoybeanGlycine maxt0
- Treatment
- msbB deletione0
- Interactor
- rhizobiae0symbiont
- Gene
- msbBe0
- Outcome
- nitrogen fixation capacitye0
- Direction
- losse0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“msbB deletion led to the formation of small and ineffective root nodules without colonization of rhizobia, thereby causing a loss of nitrogen fixation capacity”
t0“Soybean”
Claim · model-written summary
HH103Ω msbB inoculation may impair early symbiotic signaling in soybean roots.
- Taxon
- SoybeanGlycine maxt0
- Organ / stage
- soybean roote0
- Treatment
- HH103Ω msbB inoculatione0
- Interactor
- HH103Ω msbBe0symbiont
- Gene
- msbBe0
- Outcome
- early symbiotic signalinge0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“HH103Ω msbB inoculation may impair early symbiotic signaling and trigger a localized defense response in the soybean root”
t0“Soybean”
Claim · model-written summary
HH103Ω msbB inoculation may trigger a localized defense response in soybean roots.
- Taxon
- SoybeanGlycine maxt0
- Organ / stage
- soybean roote0
- Treatment
- HH103Ω msbB inoculatione0
- Interactor
- HH103Ω msbBe0symbiont
- Gene
- msbBe0
- Outcome
- localized defense response in the soybean roote0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“HH103Ω msbB inoculation may impair early symbiotic signaling and trigger a localized defense response in the soybean root”
t0“Soybean”
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