Gene Expression and Molecular Modifications Associated with Plant Responses to Infection by Arbuscular Mycorrhizal Fungi

Abstract

Microorganisms that colonize living plant tissues generally show a relatively restricted host range, but the striking feature of arbuscular mycorrhizal fungi is their ability to form a symbiotic association with roots of the large majority of terrestrial plant species. Likewise, the ancestral nature of arbuscular mycorrhiza [1] makes them a remarkable example of reciprocal cellular and physiological compatibility between plant and fungal taxa that must have been established early during land colonization and maintained through evolution. In spite of the widespread occurrence of arbuscular mycorrhiza, analyses into the molecular mechanisms and genetic determinants involved are still in their infancy due to the complexity of symbiont interactions and the incalcitrance of the fungal partner to pure culture. We have adopted two strategies to investigate plant processes regulating symbiotic fungus-root interactions: firstly, by probing tissues for molecular events that may be in common with other plant-microbe associations and, secondly, by characterizing of genes and gene products specific to arbuscular mycorrhiza. In the present paper we discuss recent data and speculate about the plant's role in establishment of the symbiotic state and in control over fungal development in arbuscular mycorrhiza.