Robust banded protoxylem pattern formation through microtubule-based directional ROP diffusion restriction

• Published in: Journal of theoretical biology Vol. 502; p. 110351
• Main Authors: Jacobs, Bas, Molenaar, Jaap, Deinum, Eva E.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 07.10.2020
• Subjects: Anisotropic diffusion; Partial differential equations; ROP patterning; Partial differential equations; Anisotropic diffusion; ROP patterning
• ISSN: 0022-5193; 1095-8541; 1095-8541
• DOI: 10.1016/j.jtbi.2020.110351

•We model ROP patterning in protoxylem development as a reaction-diffusion process.•Microtubules could act as an anisotropic diffusion barrier to orient the ROP pattern.•Directional diffusion restriction of active ROP yields a pattern of oriented bands.•The pattern orienting mechanism only works on curved features, not straight lines. In plant vascular tissue development, different cell wall patterns are formed, offering different mechanical properties optimised for different growth stages. Critical in these patterning processes are Rho of Plants (ROP) proteins, a class of evolutionarily conserved small GTPase proteins responsible for local membrane domain formation in many organisms. While te spotted metaxylem pattern can easily be understood as a result of a Turing-style reaction-diffusion mechanism, it remains an open question how the consistent orientation of evenly spaced bands and spirals as found in protoxylem is achieved. We hypothesise that this orientation results from an interaction between ROPs and an array of transversely oriented cortical microtubules that acts as a directional diffusion barrier. Here, we explore this hypothesis using partial differential equation models with anisotropic ROP diffusion and show that a horizontal microtubule array acting as a vertical diffusion barrier to active ROP can yield a horizontally banded ROP pattern. We then study the underlying mechanism in more detail, finding that it can only orient curved pattern features but not straight lines. This implies that, once formed, banded and spiral patterns cannot be reoriented by this mechanism. Finally, we observe that ROPs and microtubules together only form ultimately static patterns if the interaction is implemented with sufficient biological realism.