Spatial regularity control of phyllotaxis pattern generated by the mutual interaction between auxin and PIN1

Area of Science:

• Plant Biology
• Developmental Biology
• Mathematical Modeling

Background:

• Phyllotaxis, the arrangement of leaves on a plant stem, exhibits beautiful geometric patterns.
• This pattern arises from the interaction of the plant hormone auxin and its efflux carrier PIN1, forming regular auxin maxima.
• The precise molecular mechanism controlling this spatial regularity remains largely unknown.

Purpose of the Study:

• To investigate the molecular mechanisms underlying the spatial regularity of auxin maxima in phyllotaxis.
• To explore how realistic models, including the extracellular region, affect pattern formation.
• To identify potential unknown molecular components involved in phyllotaxis regulation.

Main Methods:

• Development and analysis of mathematical models based on auxin-PIN1 interactions.
• Utilized linear stability analysis and numerical simulations in both one and two dimensions.
• Introduced a hypothetical diffusible molecule to test feedback interactions with auxin-PIN1 dynamics.

Main Results:

• Simplified models reproduce spatial regularity, but realistic models including the extracellular region fail to do so.
• The introduction of the extracellular region disrupted pattern regularity, suggesting an unknown regulatory mechanism.
• A hypothesized diffusible molecule, mediating signaling from auxin to PIN1 polarization, successfully restored regular patterns.

Conclusions:

• The study theoretically predicts the existence of a crucial, yet undiscovered, diffusible molecule in phyllotaxis.
• This molecule is essential for mediating auxin-PIN1 interactions and establishing the regular pattern of leaf primordia.
• Further experimental investigation is needed to identify this pivotal molecule and confirm its role.