Tansley Review No. 82. Strategies of arbuscular mycorrhizal fungi when infecting host plants

summary Arbuscular mycorrhizal (AM) fungi are ancient Zygomycetes, thought to have colonized the first land plants; today, they are associated with the roots of about 80% of plant species. The symbiosis they form is potentially valuable not only for developmental programmes based on low‐input agriculture, but also as a complex experimental model, where both fungal and host plant growth are regulated. Here we review some recent progress m the area of cell and molecular biology of arbuscular mycorrhizas. Particular attention is given to strategies followed by AM fungi when, as obligate biotrophs, they establish a successful symbiosis with their host plants. Four topics are analysed: (i) parameters controlling fungal growth in the absence and presence of the host root, Le. events of DNA replication and timing of the cell cycle; (ii) mechanical and enzymatic mechanisms which allow the fungus to colonize root tissues, maintaining host viability; (iii) morphological changes induced by AM fungus host cells and, in particular, the formation de novo of a subcellular compartment termed the interface, and (iv) modifications of plant gene expression during fungal colonization, including those involving structural, symbiotic and defence‐related genes.ContentsSummary 3 I. Introduction 3 II. Fungal growth and activatioti of the cell cycle 5 III. Molecular basis of the colonization process 9 IV. Plant and fungal morphogenesis during the infection process 12 V. AM fungi change the pattern of gene expression in host plants 17 VI. Conclusions 18Acknowledgements 470References