Competence for transcellular infection in the root cortex involves a post-replicative, cell-cycle exit decision in...

Area of Science:

• Plant Biology
• Microbiology
• Cell Biology

Background:

• Root nodule symbiosis (RNS) is crucial for nitrogen fixation in legumes.
• RNS requires host root cells to accommodate rhizobia, involving cell division and differentiation.
• Previous studies suggested cell cycle arrest during early infection, but cellular details were lacking.

Purpose of the Study:

• To investigate the cell cycle status of root cortex cells during RNS at cellular resolution.
• To identify specific cell cycle events associated with rhizobial infection thread progression.
• To elucidate the molecular mechanisms underlying host cell preparation for symbiosis.

Main Methods:

• Utilized a dual-color Medicago histone reporter to distinguish mitotic and endoreduplication activities.
• Employed advanced imaging techniques to visualize deep root tissues and infection threads.
• Applied fluorescent reporters to track cell cycle phase progression (G2/M transition).

Main Results:

• Identified a distinct cell cycle stage in infected cortical cells compared to adjacent cells.
• Observed nuclear widening and chromatin rearrangements in infected cells, indicative of cell cycle exit.
• Confirmed reduced proliferation potential and modulation of the G2/M transition in successful infection events.

Conclusions:

• Rhizobial infection involves specific cell cycle modifications in host root cells.
• A pre-mitotic cell cycle arrest or exit is a key event for successful rhizobial delivery.
• The NF-YA1 transcription factor may play a role in regulating the G2/M transition during RNS.