A realistic algorithm for microtubule-based nucleation reveals large sensitivity to cell geometry of the plant cortical array

The self-organisation of cortical microtubules into aligned arrays plays a key role in plant cell morphogenesis and organismal growth. Computational studies have highlighted the impact of simulation domain topology and directional biases in microtubule dynamics on this alignment. Despite this, simulating microtubule nucleation has been challenging for years, as modelling nucleation of new microtubules from extant microtubules lead to inhomogeneity within cortical arrays, characterized by large empty spaces and few densely populated areas. We introduce a novel, efficient algorithm that realistically simulates microtubule nucleation by approximating the diffusion of nucleation complexes, which yields uniform arrays by maintaining realism in the nucleation process without the computational burden of explicit diffusion simulation. With our model, we show that strong biases towards specific orientations of alignment in self-organised arrays can emerge naturally when nucleation is modelled with enhanced biological realism. More specifically, we observe that cell geometry has a strong influence in driving the array towards a preferred transverse orientation. Our approach opens up new avenues for quantitative comparisons of different factors influencing array orientation and, as such, can be a powerful tool for re-assessing conclusions about the drivers of microtubule alignment in plant cells.