Cell type-specific protein and transcription profiles implicate periarbuscular membrane synthesis as an important carbon sink in the mycorrhizal symbiosis

The development of an arbuscular mycorrhizal (AM) symbiosis is a non-synchronous process with typical mycorrhizal root containing different symbiotic stages at one time. Methods providing cell type-specific resolution are therefore required to separate these stages and analyze each particular structure independently from each other. We established an experimental system for analyzing specific proteomic changes in arbuscule-containing cells of Glomus intraradices colonized Medicago truncatula roots. The combination of laser capture microdissection (LCM) and liquid chromatography-tandem mass chromatography (LC-MS/MS) allowed the identification of proteins with specific or increased expression in arbuscule-containing cells. Consistent with previous transcriptome data, the proteome of arbuscule-containing cells showed an increased number of proteins involved in lipid metabolism, most likely related to the synthesis of the periarbuscular membrane. In addition, transcriptome data of non-colonized cells of mycorrhizal roots suggest mobilization of carbon resources and their symplastic transport toward arbuscule-containing cells for the synthesis of periarbuscular membranes. This highlights the periarbuscular membrane as important carbon sink in the mycorrhizal symbiosis.