Nutrient sensing in Leishmania: Flagellum and cytosol

Parasites are by definition organisms that utilize resources from a host to support their existence, thus, promoting their ability to establish long‐term infections and disease. Hence, sensing and acquiring nutrients for which the parasite and host compete is central to the parasitic mode of existence. Leishmania are flagellated kinetoplastid parasites that parasitize phagocytic cells, principally macrophages, of vertebrate hosts and the alimentary tract of sand fly vectors. Because nutritional supplies vary over time within both these hosts and are often restricted in availability, these parasites must sense a plethora of nutrients and respond accordingly. The flagellum has been recognized as an “antenna” that plays a core role in sensing environmental conditions, and various flagellar proteins have been implicated in sensing roles. In addition, these parasites exhibit non‐flagellar intracellular mechanisms of nutrient sensing, several of which have been explored. Nonetheless, mechanistic details of these sensory pathways are still sparse and represent a challenging frontier for further experimental exploration. This article reviews the current status of nutrient sensing in Leishmania parasites, with reference to mechanisms that likely originate in both the flagellum and the cytoplasm. A few examples of other sensory pathways that have been explored in African trypanosomes are also introduced for illustrative purposes.