Conserved mechanical hallmark guides four-way junction avoidance during plant cytokinesis

Area of Science:

• Cell biology
• Plant development
• Mechanobiology

Background:

• Topologically stable cell junctions are crucial for organ development in multicellular organisms.
• Accurate positioning of cell division is essential to prevent unstable four-way junctions, especially in walled cells that cannot migrate.
• The microtubule preprophase band (PPB) is known to guide cell division, but its absence in mutants shows minimal defects, suggesting alternative mechanisms.

Purpose of the Study:

• To investigate the PPB-independent mechanism guiding cell division site selection in plants.
• To identify the molecular players and physical principles involved in preventing four-way junction formation during cytokinesis.

Main Methods:

• Analysis of Arabidopsis mutants, specifically sac9-3, impaired in phosphoinositide phosphatase activity.
• Utilizing numerical simulations to model mechanical stress and elastic energy accumulation in cell walls.
• Perturbation of root mechanical homeostasis to observe effects on junction formation.

Main Results:

• A PPB-independent mechanism guides cell division sites near tricellular junctions.
• The phosphoinositide phosphatase SAC9 is critical for this process; sac9-3 mutants exhibit abnormal cell plate attachment.
• Numerical simulations indicate that mechanical stress and elastic energy in cell walls act as positional cues for tricellular junctions.
• Disrupting root mechanical homeostasis leads to the formation of unstable four-way junctions.

Conclusions:

• Cells utilize subcellular mechanical hallmarks to avoid forming unstable four-way junctions during cytokinesis.
• SUPPRESSION OF ACTIN 9 (SAC9) plays a key role in interpreting these mechanical cues for proper cell division positioning.
• This study reveals a novel mechanosensitive pathway for cell division site selection in plants, distinct from PPB-mediated guidance.