Laser microdissection as a tool to study fungal gene expression in mycorrhizal endosymbioses

Laser microdissection (LMD) is a microscopy technique that, through the collection of specific cell-type populations from sections of heterogeneous tissues, allows the subsequent extraction of nucleic acids as well as primary and secondary metabolites. In plants, LMD was widely used to study cell-specific gene expression during symbiotic interactions with other organisms, including mycorrhizal fungi. In particular, LMD was extensively used to study cell-specificity in gene expression profiles in arbuscular mycorrhizal (AM) and orchid mycorrhizal (ORM) interactions. These earlier studies were mainly focused on the identification of functional markers in plant cells containing intracellular fungal structures, i.e. arbuscules, the typical structures in AM, and coils, typical of ORM. Several plant and fungal genes coding for nutrient transporters were identified in these cells thanks to LMD, suggesting that symbiotic nutrient exchange is cell specific. In the absence of a stable transformation protocol for the expression of tagged genes in the mycorrhizal fungal partner, LMD protocols represent a useful tool to study fungal gene expression in specific cell-type populations inside symbiotic plant tissues.