Microscopic Techniques Coupled to Molecular and Genetic Approaches to Highlight Cell-Type Specific Differences in Mycorrhizal Symbiosis

Mycorrhizal symbioses, i.e., the associations between plant roots and soil symbi- otic fungi, are an essential feature of the biology of most terrestrial plants in a wide range of terrestrial ecosystems. Both plant and fungal genes involved in the dialogue between the two partners and in the symbiotic lifestyle have been identified in different mycorrhizal interactions. However, a mycorrhizal root represents a complex heterogeneous mixture of different cell and tissue types of both symbiotic partners, which complicates the interpretation of whole root expression profiling. Thus, examination of the process at the molecular level suffers from the use of whole organs since cell-type-specific differences might be masked. The aim of this chapter is to describe the main approaches that have been used to study cell specificity in mycorrhizal interactions, mainly considering AM symbiosis on which most of the experiments have been performed. Attention will be focused on the relevant advancements in knowledge obtained thanks to the application of microscopic techniques coupled to molecular and genetic approaches, such as in situ hybridization, approaches involving plant transforma- tion, and laser microdissection (LMD), to study cell specificity in symbiotic tissues.