Mechanical Conflicts in Twisting Growth Revealed by Cell-Cell Adhesion Defects

Area of Science:

• Plant biology
• Cellular mechanics
• Developmental biology

Background:

• Plant organs often exhibit twisted growth patterns.
• Mutants with altered microtubule dynamics show constitutive twisting.
• The mechanisms linking molecular defects to large-scale twisting remain unclear.

Purpose of the Study:

• To investigate the role of cell-cell adhesion in plant organ twisting.
• To determine if mechanical coupling between cells is essential for twisting phenotypes.
• To test the hypothesis that supracellular torsion relaxes cell-level mechanical conflicts.

Main Methods:

• Utilized Arabidopsis mutants: quasimodo1 (qua1) with adhesion defects and spiral2/tortifolia1 (spr2) with helical growth.
• Generated double mutants (qua1-1 spr2-2) to assess the combined effects.
• Analyzed growth phenotypes of hypocotyls and leaves.
• Manipulated medium matrix potential to alter inter-cellular forces.

Main Results:

• qua1-induced cell-cell adhesion defects restored straight growth in the qua1-1 spr2-2 double mutant.
• Detached cells in the double mutant showed helical growth, indicating lack of mechanical coupling.
• Reducing medium matrix potential also restored straight hypocotyl growth in the double mutant.
• Straight growth was observed in both hypocotyls and leaves of the double mutant.

Conclusions:

• Cell-cell adhesion is crucial for transposing local mechanical conflicts into macroscopic twisting.
• Supracellular torsion in mutants like spr2 likely arises from the relaxation of mechanical conflicts via global organ torsion.
• Mechanical coupling between cells plays a significant role in regulating plant organ morphology.