Processes regulating pollen germination, growth, guidance and sperm delivery are considered major hybridization controls in nature and contribute to reproductive success as well as to isolation and speciation. Dresselhaus et al. show how maize (Zea mays) can be developed as a model to understand the underlying molecular mechanisms of these processes. Focusing on this species, they provide an overview of our current understanding of the pollen tube pathway and associated intra- and interspecific crossing barriers in Poaceae.
