The molecular and cellular mechanism by which the kinesin nKCBP is revealed by microorganisms regulates symbiosis in rhizobia

On November 1, 2022, the Kong Zhaosheng Research Group of the Institute of Microbiology of the Chinese Academy of Sciences published a research paper in Nature Plants (A Legume Kinesin Controls Vacuole Morphogenesis for Rhizobia Endosymbiosis), revealing the molecular and cellular mechanism
by which the kinesin nKCBP regulates symbiosis in rhizobia.

KCBP (Kinesin-like Calmodulin-Binding Protein) is a unique microtubule motor protein of plants, which has the ability to bind microtubules and microfilaments at the same time, and regulate the dynamic remodeling of the cytoskeleton and the construction of
cell morphology.
Interestingly, the KCBP gene doubled in legumes, and the copy nKCBP enriched in the nodules evolved and used by rhizobia to regulate nodular nitrogen
fixation.
Tribulus terrestris (Medicago truncatula) nkcbp mutant was obtained using gene editing techniques, showing growth defects (Figure 1a) and a significant decrease in nitrogen fixation capacity (Figure 1b).

Further observation of semi-thin sections and ultra-thin sections of nodules showed that the infected cells of wild-type nodules had typical central large vacuoles (Figures 1c and 2a), while NKCBP mutants contained a large number of randomly distributed small unfused vacuoles (Figures 1d and 2b), and even some infected intracellular symbionts could not differentiate and the symbiont membrane thickened
.
The structure of wild-type and mutant vacuoles was reconstructed in three dimensions using Automatic collector of ultrathin sections scanning electron microscopy (AutoCUTS-SEM) (Figure 2).

Combined with live-cell imaging and immunofluorescence staining, nKCBP has conserved biochemical functions while binding microtubules and microfilaments
.
It was further found that compared with the wild type, the cytoskeletal radial arrangement in NKCBP mutant infected cells was disrupted and showed a random and disordered arrangement pattern
.
In summary, nKCBP regulates vacuolegenesis and symbiotic interface formation by regulating cytoskeletal dynamic remodeling (Figure 3), thereby controlling intraneosis and efficient nitrogen
fixation in rhizobia.