Seminario “Mycorrhizas: structural characteristics of the plant-fungus interface”

Mycorrhizas: structural characteristics of the plant-fungus interface



R. Larry Peterson, Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada


Roots of over 90% of vascular plants, including most commercially important forest
and crop species, are associated with fungal symbionts, forming mycorrhizas.
Mycorrhizas are categorized primarily on the interaction between the plant
group and particular fungal species, resulting in characteristic changes in the
morphology and cytology of both symbionts. A critical development in all
mycorrhiza categories is the nutrient-exchange interface between the symbiotic
partners. With the exception of ectomycorrhizas, in which fungal hyphae occupy
the apoplast external to epidermal and cortical cell walls, the other
mycorrhiza categories involve the penetration of plant cell walls by fungal
hyphae and the formation of highly modified fungal structures. However, in all
of the latter cases studied to date, hyphae are separated from the plant cell
cytoplasm by host-derived membrane (perifungal membrane) and a host-derived
interfacial matrix consisting of molecules found in primary walls of plant
cells. This matrix, which varies in composition depending on the mycorrhiza
category, is deposited between the perifungal membrane and the hyphal wall
forming an apoplastic compartment. The formation of the perifungal membrane and
the deposition of matrix components into the apoplastic compartment likely
involve the host cytoskeleton. Regardless of the structural nature of the
nutrient-exchange interface, nutrients must pass into the symplast of both
partners at some point. Therefore, there is considerable interest in
determining the modifications in host and fungal cell walls during the
colonization process and in identifying the membrane transporters involved. Our
current research involves an enigmatic group of achlorophyllous plant species
(mycoheterotrophs) that depend on fungal links to photosynthetic plants for
their carbon needs. Some of these form unique nutrient exchange interfaces.