haustorium: one construct, many systems

In biotrophic fungi a haustorium is a specialised hypha that pushes into a living host cell and, without killing it, invaginates the host membrane to build an intimate feeding interface across which sugars and amino acids are drawn from the plant. It is the defining organ of rusts, powdery mildews, and downy mildews, which depend on keeping the host alive. Voegele and Mendgen's Rust haustoria: nutrient uptake and beyond shows it is not only an absorptive organ but a site of transport and signalling. The referent is a host-penetrating absorptive organ of a fungus.[1]

Unit

The host-penetrating feeding structure and its uptake across the host interface

Recovery means

Not applicable

Measured by

Studied by microscopy of the host–parasite interface and by assaying nutrient transporters expressed in the haustorium

Parasitic plants independently evolved an organ of the same name and role: the haustorium is the invasive structure a plant such as dodder, broomrape, or witchweed drives into the stem or root of a host to tap its vascular tissue and withdraw water, nutrients, and sometimes signalling molecules. It is the organ that defines plant parasitism, forming a living bridge between two plants. Yoshida and colleagues' The haustorium, a specialized invasive organ in parasitic plants reviews its development and function. This is genuinely the same construct as the fungal haustorium, a host-penetrating absorptive organ, reached by a separate evolutionary route.[2]

Unit

The host-penetrating organ bridging parasite and host vasculature

Recovery means

Not applicable

Measured by

Characterised by its anatomy at the host connection and by tracking water and solute transfer across it