Carbohydrate metabolism in ectomycorrhizas: gene expression, monosaccharide transport and metabolic control

Abstract

SummaryEctomycorrhizas are mutalistic symbiotic associations formed between fine roots of higher plants, mostly trees, and a wide range of soil ascomycetes and basidiomycetes. It is commonly accepted that there is mutual benefit to the partners, due to the exchange of plant-derived carbohydrates for amino acids and nutrients supplied by the fungus. While the major concepts of mycorrhizal functioning (exchange of nutrients and metabolites) were proposed in the 1960s, their verification at the molecular level started approximately 10 years ago. This review covers concepts at the molecular level concerned with the fungal carbohydrate supply in symbiosis. We discuss: strategies used by host plants to compensate (and perhaps restrict) carbohydrate drain to the fungal partner; fungal mechanisms that generate strong monosaccharide sinks in colonized plant roots (the formation of a strong carbohydrate sink is a prerequisite for efficient fungal carbohydrate support by the plant partner); and the impact of apoplastic hexose concentration on the regulation of fungal metabolism in symbiosis, since monosaccharides not only serve as nutrients but also as a signal that regulates gene expression.

Application of Laser Microdissection to plant pathogenic and symbiotic interactions

“…plantÁplant pathogenic interactions (Pe´rez-de-Luque et al 2008) and root nodules). Considering the tissue and cellular complexity of an ectomycorrhiza, LM technology could also be very useful to collect the two specific fungal compartments separately (the mantle and the Hartig net) which are expected to be functionally different, at least in terms of nutrient uptake and transport (Nehls et al 2001).…”

Diversity and classification of mycorrhizal associations

“…Hawksworth et al, 1995), but are of little value as they do not exclude pathogenic associations. Mycorrhizas are now considered to differ primarily from other plant-fungus associations because they are intimate associations with a specialised interface where exchange of materials occurs between living cells (Nehls et al, 2001 ;Pfeffer, Bago & Shachar-Hill, 2001). Most mycorrhizas occur in roots, which evolved to house fungi , but they also occur in the subterranean stems of certain plants and the thallus of bryophytes (Smith & Read, 1997;Read et al, 2000).…”

Variability of inorganic nutrient concentrations in leaves

“…The nutritional benefits that mycorrhizal symbioses confer on each partner hinge on the structural and physiological intricacy between the symbionts, and therefore detailed information on metabolism, transport ( Nehls et al , 2001a) and functional anatomy of intact systems is required. In addition, elucidation of the function of the hundreds of known and unknown genes analysed by transcript profilings and proteomics may be nicely supplemented by the simultaneous analysis of the metabolome, the latter changing according to the physiological and developmental state of a cell, tissue, organ, or organism.…”