A Lipopolysaccharide Synthesis Gene rfaD from Mesorhizobium huakuii Is Involved in Nodule Development and Symbiotic Nitrogen Fixation

Abstract

Rhizobium lipopolysaccharide (LPS) is an important component of the cell wall of gram-negative bacteria and serves as a signal molecule on the surface of rhizobia, participating in the symbiosis during rhizobia–legume interaction. In this study, we constructed a deletion mutant of ADP-L-glycerol-D-mannoheptosyl-6-exoisomerase (rfaD) of Mesorhizobium huakuii 7653R and a functional complementary strain. The results showed that the deletion of rfaD did not affect the free-living growth rate of 7653R, but that it did affect the LPS synthesis and that it increased sensitivity to abiotic stresses. The rfaD promoter-GUS reporter assay showed that the gene was mainly expressed in the infection zone of the mature nodules. The root nodules formation of the rfaD mutant was delayed during symbiosis with the host plant of Astragalus sinicus. The symbiotic phenotype analyses showed that the nodules of A. sinicus lost symbiotic nitrogen fixation ability, when inoculated with the rfaD mutant strain. In conclusion, our results reveal that the 7653R rfaD gene plays a crucial role in the LPS synthesis involved in the symbiotic interaction between rhizobia and A. sinicus. This study also provides new insights into the molecular mechanisms by which the rhizobia regulate their own gene expression and cell wall components enabling nodulation in legumes.

Hopanoid lipids promote soybean –Bradyrhizobium symbiosis

“…5F ). Genes involved in lipopolysaccharide (LPS) biosynthesis and symbiosis, such as rafD and rafE ( 32 ), also are among the downregulated DEGs ( Fig. 5D ).…”

Hopanoid lipids promote soybean-Bradyrhizobiumsymbiosis

“…5C ). Genes involved in lipopolysaccharide (LPS) biosynthesis and symbiosis, such as rafD and rafE (30), also are among the down-regulated DEGs ( Fig. 5B ).…”

Genetic Analysis of the ts-Lethal Mutant Δpa0665/pTS-pa0665 Reveals Its Role in Cell Morphology and Oxidative Phosphorylation in Pseudomonas aeruginosa

“…Impairment of pa4067/oprG Possibly Linked to the Altered Morphology of ∆pa0665/pTS-pa0665 Mutant at 42 • C Transcriptomic analyses revealed that pa3337/rfaD and pa4067/oprG were among the top seven significantly downregulated genes (Figure 6C), both critical for the structural integrity of the bacterial outer membrane. oprG plays a key role in forming outer membrane channels in Gram-negative bacteria, crucial for molecular transport and affecting bacterial virility and antibiotic resistance [24], while rfaD is vital for lipopolysaccharide (LPS) biosynthesis, a key outer membrane component in Gram-negative bacteria [25,26]. To investigate the impact of disrupting pa3337/rfaD and pa4067/oprG on cellular morphology, we constructed knockout plasmids containing sequences approximately 500 bp identical to the N-terminal coding sequences of pa3337/rfaD and pa4067/oprG.…”