Cellular programs for arbuscular mycorrhizal symbiosis.

In arbuscular mycorrhizal (AM) symbiosis, AM fungi colonize root cortical cells to obtain carbon from the plant, while assisting the plant with the acquisition of mineral nutrients from the soil. Within the root cells, the fungal hyphae inhabit membrane-bound compartments that the plant establishes to accommodate the fungal symbiont. Recent data provide new insights into the events associated with development of the symbiosis including signaling for the formation of a cellular apparatus that guides hyphal growth through the cell. Plant genes that play key roles in a cellular program for the accommodation of microbial symbionts have been identified. In the inner cortical cells, tightly regulated changes in gene expression accompanied by a transient reorientation of secretion, enables the cell to build and populate the periarbuscular membrane with its unique complement of transporter proteins. Similarities between the cellular events for development of the periarbuscular membrane and cell plate formation are emerging.