One organ to infect them all: the Cuscuta haustorium

Research on the parasitic plant genus Cuscuta has flourished since the genomes of several of its species were published. Most of the research revolves around the iconic infection organ that secures the parasite's sustenance: the haustorium. Interest in understanding the structure-function-regulation relationship of the haustorium is based as much on the wish to find ways to keep the parasite under control as on the opportunities it offers to shed light on various open questions in plant biology.

This review will briefly introduce parasitism among plants, using the genus Cuscuta as the main example, before presenting its haustorium alongside the terminology that is used to describe its architecture. Possible evolutionary origins of this parasitic organ are presented. The haustorium is then followed from its initiation to maturity with regard to the molecular landscape that accompanies the morphological changes and in light of the challenges it must overcome before gaining access to the vascular cells of its hosts. The fact that Cuscuta has an unusually broad host range stresses how efficient its infection strategy is. Therefore, particular consideration will be given in the final section to a comparison with the process of grafting, being the only other type of tissue connection that involves interspecific vascular continuity.

Studies on Cuscuta haustoriogenesis have revealed many molecular details that explain its success. They have also unearthed some mysteries that wait to be solved. With a better understanding of the complexity of the infection with its combination of universal as well as host-specific elements that allow Cuscuta to parasitize on a wide range of host plant species, we may be many steps closer to not only containing the parasite better but also exploiting its tricks where they can serve us in the quest of producing more and better food and fodder.