Diversification of budding yeast polarization dynamics after compensatory experimental evolution

Essential cellular processes evolve under strong selection, yet protein networks underlying conserved functions can vary substantially. To what extent evolution constrains the intracellular dynamics of proteins performing essential functions is currently largely unknown. Here, we characterize budding yeast polarization phenotypes along a previously established evolutionary recovery trajectory, compensating for the loss of near-essential polarity gene BEM1. Through quantitative live cell imaging, we show that loss of BEM1 weakens and destabilizes polarization. Surprisingly, in recovered evolved lineages, protein dynamics change significantly compared to the ancestor: most notably, presence of main regulator Cdc42-GTP is strongly decreased, while polarisome member Spa2 localizes more slowly into mobile foci. Although separate phenotypic characteristics are only weakly constrained, we find evidence of effective protein-independent localization modes, revealing signs of convergence along the evolutionary trajectory. Together, our results show that evolution can restore global cellular function without conserving microscopic organization, instead giving rise to novel molecular phenotypes.