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Lectin receptor kinases and Cell wall-sensing mechanisms

Contact  : mail to Hervé CANUT

Our group investigates communication between the cell wall and the cytoplasm of plants. One focus is to decipher the functions of lectins in the model plant Arabidopsis thaliana.

Lectins are widespread proteins in all kingdoms of life. They are able to bind mono-or oligosaccharides in a reversible way and to decipher the information contained in these complex structures. Lectins, mainly originating from plants, find large applications in bioscience and biomedicine. From the original applications in blood banks, recent progress has been made in unravelling their effects, often beneficial, on tumours and in cancer therapy. Also, lectins are fundamental to plant life and play important roles in cell communication, development and natural defence strategies.

Cell walls are complex structures made of cellulose, hemicelluloses, pectins and proteins secreted by the cell, so setting up a rigid and continuous structure within the plant tissues. Cell walls are dynamic structures, sources of chemical or mechanical signals. In A. thaliana, the lectins are present in the cell walls both as soluble proteins weakly bound to the wall (Lecs), and as chimeric proteins located at the plasma membrane : lectins are then the extracellular domain of lectin receptor kinases (LecRKs).

We showed that, in A. thaliana, cell wall-plasma membrane contacts [1-white arrowheads] are set up by protein-protein interactions involving the recognition of the Arg-Gly-Asp (RGD) motif. LecRK-I.9 (At5g60300) is a candidate to be a linker between plasma membrane and cell wall. LecRK-I.9 belongs to the legume-type lectin family [2]. Recent results showed that LecRK-I.9 affects resistance of A. thaliana to Pseudomonas syringae pv. tomato (Pst), a bacterial pathogen and to Phytophthora infestans (Bouwmeester et al. 2011, Balagué et al. 2016).

Besides, our analysis of the cell wall proteome of elongating cells revealed several Lecs (Irshad et al. 2008). From amino acid sequences analysis, the legume lectin domains of both Lecs and LecRKs are closely related and form a cluster in phylogenic trees. Finally, LecRK-I.9 promoter-GUS reporter gene fusions revealed that the LecRK-I.9 promoter activity is the highest in the apex of the main root and absent from the primordia of lateral roots [3].

The aim of the project is to elucidate the role of Lecs/LecRKs in A. thaliana. A combination of biochemistry and functional genomics approaches will be carried out to identify the Lecs/LecRKs extracellular ligands and to unravel the functions of lectins. We assume that Lecs/LecRKs are involved in the detection of pathogens, but also in the assembly and the remodelling of the cell wall polysaccharides. In particular, Lecs/LecRKs could act as sensors and be sentinels reporting the cell wall integrity.

ANR : WALLARRAY2 (2011-2014)

Collaborations :
Francine GOVERS : Laboratory of Phytopathology, Wageningen University, Wageningen, Pays Bas.
Claudine BALAGUE, Dominique ROBY : LIPM, Auzeville, France.