Applying microfluidics to studying polar growth of infectious hyphae from Ustilago maydis

A hallmark for fungal pathogens is a morphological switch from yeast-like to hyphal growth. This hold true for human pathogens like Cryptococcus neoformans or Candida albicans as well as for plant pathogens like Ustilago maydis. In the latter, the morphological transition is particularly important during the formation of infectious hyphae. These are essential to penetrate the plant for infection. Long distance transport along microtubules is important for hyphal growth. Key carriers are early endosomes that serve as multi-purpose platform for the transport of numerous cargos such as mRNAs, ribosomes, heteromeric protein complexes as well as whole organelles such as peroxisomes. We uncovered that the RNA-binding protein Rrm4 is essential for endosomal transport of mRNAs and associated ribosomes. Loss of Rrm4 causes defects in polar growth i.e. hyphae exhibit aberrant bipolar growth. A limitation of our current experimental set-up is the fact that we can only observe hyphal growth for a short period of time and without additional nutrient supply. Here, we present a microfluidic approach to study endosomal RNA transport during hyphal growth in the time range of hours. Thereby, we will be able to follow this important biological process with unprecedented spatial and temporal resolution in the context of an experimentally well-controlled environment.