Ectopic activation of cortical cell division during the accommodation of arbuscular mycorrhizal fungi

Abstract

Arbuscular mycorrhizas (AMs) between plants and soil fungi are widespread symbioses with a major role in soil nutrient uptake. In this study we investigated the induction of root cortical cell division during AM colonization by combining morphometric and gene expression analyses with promoter activation and protein localization studies of the cell-plate-associated exocytic marker TPLATE. Our results show that TPLATE promoter is activated in colonized cells of the root cortex where we also observed the appearance of cells that are half the size of the surrounding cells. Furthermore, TPLATE-green fluorescent protein recruitment to developing cell plates highlighted ectopic cell division events in the inner root cortex during early AM colonization. Lastly, transcripts of TPLATE, KNOLLE and Cyclinlike 1 (CYC1) are all upregulated in the same context, alongside endocytic markers Adaptor-Related Protein complex 2 alpha 1 subunit (AP2A1) and Clathrin Heavy Chain 2 (CHC2), known to be active during cell plate formation. This pattern of gene expression was recorded in wild-type Medicago truncatula roots, but not in a common symbiotic signalling pathway mutant where fungal colonization is blocked at the epidermal level. Altogether, these results suggest the activation of cell-division-related mechanisms by AM hosts during the accommodation of the symbiotic fungus.

Local endoreduplication as a feature of intracellular fungal accommodation in arbuscular mycorrhizas

“…ROC lines, already available in the laboratory (Chabaud et al, 2011;Genre et al, 2013), expressed a nuclear localized cameleon YC2.1 construct, and were propagated on M medium (B ecard & Fortin, 1988) at 25°C in the dark, in vertically oriented petri dishes to favor a regular fishbone-shaped root system (Chabaud et al, 2002). Explants with consistent morphology and an identical number of lateral roots were chosen for all ROC-based experiments (Russo et al, 2019).…”

Symbiosis: Plasmodesmata Link Root-Nodule Organogenesis with Infection

“…Root-nodule symbiosis has evolved by co-opting signaling mechanisms from the more ancient arbuscular mycorrhizal symbiosis between plants and nutrientdelivering fungi of the glomeromycotina [13,14]. It was recently reported that attachment of the fungus to the root surface induces cell division in the cortex [15], similar to the initial cell-division events observed during rhizobial infection and nodulation. Furthermore, priming of cells that neighbor colonized cells has been observed [12,16].…”

A Homeotic Mutation Changes Legume Nodule Ontogeny into Actinorhizal-Type Ontogeny

“…However, it was recently suggested that cell-division-related processes also occur in cortical cells during the accommodation of AM fungi (Russo et al, 2019).…”