Sub-cellular distribution of polyphosphoinositide suggests a role in signaling during arbuscular mycorrhiza symbiosis.
S. IVANOV (1), M. Harrison (1) (1) Boyce Thompson Institute, U.S.A.

Arbuscular mycorrhiza (AM) symbiosis is mutualistic interaction between fungi of the Glomeromycota and most families of land plants. The biotrophic AM fungi colonize root cortical cells to receive plant carbohydrates and provide the plant with mineral nutrients. Following invasion and colonization of the root cortex, highly branched fungal hyphae called arbuscules are formed inside the root cortical cells. Each arbuscule has two structural domains (trunk and branches) and is surrounded by a plant-derived membrane, the periarbuscular membrane (PAM), via which controlled exchange of nutrients and carbon sources takes place. The signaling mechanisms that regulate membrane trafficking towards developing PAM are currently unknown. Phosphoinositides are a class of minor membrane lipids that play diverse roles in membrane trafficking and these roles are often tied to their specific spatial and temporal distributions. Here we characterize the sub-cellular distribution of fluorescent protein reporters for phosphatidylinositol 4-bisphosphate (PtdIns4P), phosphatidylinositol 4,5-bisphosphate (PtdIns4,5P2), diacylglycerol (DAG) and phosphatidic acid (PA) in Medicago truncatula roots colonized by arbuscular mycorrhizal fungus Rhizophagus irregularis. We found that the reporter for PtdIns4,5P2 (GFP-PHPLCδ1) has distinct accumulation around arbuscule trunk in developing and mature arbuscules. The frequency of such accumulation is reduced in Medicago RAM1 mutant in which arbuscule development is arrested at arbuscule trunk stage. Reporters for DAG (CYS1PKC-mCherry) and PA (mCherry-PABDSpo20p) show co-localization with GFP-PHPLCδ1 suggesting that signaling via phospholipase C may occur during arbuscule development. Alternatively, based on morphological data we hypothesize that PtdIns4,5P2 accumulations may represent sites of fungal effectors activity and their delivery into the plant cell.

Abstract Number: P2-29
Session Type: Poster