Section I. Signaling Mechanisms in Mycorrhizal Symbiosis -- Section II. Mycorrhizal Fungi and Plant Defense -- Section III. Molecular Genetics of Mycorrhizal Symbiosis -- Section IV: Carbon Metabolism and Cost of Arbuscular Mycorrhizas -- Section V. Ultrastructural Changes During Mycorrhizal Symbiosis -- Section VI. Genetic Engineering of Mycorrhizal Fungi