Multimodal Sensorimotor System in Unicellular Zoospores of a Fungus

Complex sensory suites often underlie critical behaviors, including avoiding predators or locating prey, mates, and shelter. Multisensory systems that control motor behavior even appear in unicellular eukaryotes, such as Chlamydomonas, which are important laboratory models for sensory biology. However, we know of no unicellular opisthokont models that control motor behavior using a multimodal sensory suite. Therefore, existing single-celled models for multimodal sensorimotor integration are very distantly related to animals. Here, we describe a multisensory system that controls the motor function of unicellular, fungal zoospores. We find zoospores of Allomyces arbusculus exhibit both phototaxis and chemotaxis. While swimming, they move towards light and settle on cellulose membranes exuding combinations of amino acids. Furthermore, we report that closely related Allomyces species do not share this multisensory system. Instead, each possesses only one of the two modalities present in A. arbusculus. This diversity of sensory suites within Allomyces provides a rare example of a comparative framework that can be used to examine the evolution of sensory suites. The tractability of Allomyces and related fungi as laboratory organisms will allow detailed mechanistic investigations into how sensory systems may have functioned in early opisthokonts before multicellularity allowed for the evolution of specialized cell types.\n\nSummary StatementZoospores ability to detect light or chemical gradients varies within Allomyces. Here, we report a multimodal sensory system controlling behavior in a fungus, and previously unknown variation in zoospore sensory suites.