CROWN

Root-knot nematodes (RKN) are microscopic worms that parasitise plant roots and are one of the world's most important crop pests. The wide host range of these pests includes more than 5000 plant species, including most crops. Each year, root knot nematodes are responsible for more than 10 billion dollars in agricultural losses worldwide. Once inside the root, RKN induce the dedifferentiation of root vascular cells into giant, hypermetabolic and multinucleate feeding cells. The cells surrounding the giant feeding cells and the RKN larvae divide and initiate vascular differentiation, the whole forming the nematode feeding site. The formation of the feeding site leads to the appearance of root galls, which is the characteristic symptom of root knot nematode infection. Nematode-induced feeding site ontogeny provides an original pathophysiological model for studying cell wall rearrangements. Our recent paper described the induction of small non-coding RNAs, microRNAs, in galls by copper starvation and a reduced susceptibility of plants to RKN infection when plants were watered with non-toxic copper sulphate solution. In addition, preliminary results in Arabidopsis and tomato showed a decrease in copper content in galls compared to uninfected roots. These results suggest that RKN infection is associated with a decrease in copper in the gall cells. Copper microRNAs induced in galls repress the expression of genes encoding non-essential copper-binding proteins. These copper-binding proteins, such as uclacyanins or laccases, are involved in lignin deposition in root tissue. During nematode-induced feeding, the tissues surrounding the giant feeding cells are rearranged. The endodermis, a specialised cell layer reinforced by suberin deposition and a lignin band called the Casparian strip, which initially surrounded the very early developing feeding site, is degraded. This degradation of the Casparian strip occurs concurrently with the formation of the periderm from dividing pericycle cells, which exhibit lignin and suberin deposition in their cell wall. Finally, the mature nematode-induced feeding site is enclosed within a de novo formed network of xylem and phloem cells. Therefore, the RKN-induced feeding site provides an original model to study the role of copper in Casparian strip formation, cell wall remodelling and tissue rearrangement in Arabidopsis and tomato roots. The CROWN project proposes to integrate elemental analysis and advanced technologies in elemental microscopy (X-ray fluorescence imaging), omic sequencing, reverse genetics and cell biology approaches to investigate how copper depletion induced by RKN infection might affect cell wall remodelling in galls and in particular Casparian Strip degradation, peridermal lignin deposition and xylem vessel lignification. To address these questions, CROWN is bringing together experts in RKN infection, metal homeostasis and endodermal differentiation and cell wall remodelling.