Signal transduction pathways in mycorrhizal associations: Comparisons withthe Rhizobium-legume symbiosis

A number of genera of soil fungi interact with plant roots to establish sym biotic associations whereby phosphate acquired by the fungus is exchanged f or fixed carbon from the plant, Recent progress in investigating these asso ciations, designated as mycorrhizae (sing,, mycorrhiza), has led to the ide ntification of specific steps in the establishment of the symbiosis in whic h the fungus and the plant interact in response to various molecular signal s. Some of these signals are conserved with those of the Rhizobium-Iegume n itrogen-fixing symbiosis, suggesting that the two plant-microbe interaction s share a common signal transduction pathway. Nevertheless, only legume hos ts nodulate in response to Rhizobium, whereas the vast majority of flowerin g plants establish mycorrhizal associations. The key questions for the futu re are: what are the signal molecules produced by mycorrhizal fungi and how are they perceived by the plant? (C) 1998 Academic Press.