Morphological and molecular development of Terfezia claveryi ectendomycorrhizae exhibits three well-defined stages

The normal development of mycorrhizal symbiosis is a dynamic process, requiring elaborately regulated interactions between plant roots and compatible fungi, mandatory for both partners´ survival. In the present study, we further elucidated the mycorrhizal development of the desert truffles Terfezia claveryi with the host plant Helianthemum almeriense as an ectendomycorrhizal symbiosis model under greenhouse conditions. To investigate this, we evaluated the morphology of mycorrhizal colonization, concomitantly with the dynamic expression of selected marker genes (6 fungal and 11 plant genes) measured every week until mycorrhiza maturation (three months). We were able to determine 3 main stages in the mycorrhization process, 1) pre-symbiosis stage where mycelium is growing in the soil with no direct interaction with roots, 2) early symbiosis stage when the fungus spreads along the roots intercellularly and plant-fungal signaling is proceeding, and 3) late symbiosis stage where the fungus consolidates and matures with intracellular hyphal colonization; this is characterized by the regulation of cell-wall remodeling processes.