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Accueil du site > Equipes de recherche > Immunité Végétale et Effecteurs > Thèmes de recherche > Aphanomyces euteiches effectors and their role in pathogenicity

Aphanomyces euteiches effectors and their role in pathogenicity

Contact : mail to Elodie GAULIN

Plants, like animals, are exposed to a myriad of potential microbial pathogens, but diseases are still the exception, at least in natural ecosystems. Without any adaptive immune system, plants have developed an innate immune system that efficiently detects potentially dangerous microbes. One similarity between plant and animal innate immunity is that both are activated by the perception of “non-self” secreted Pathogen (or Microbial) Associated Molecular Patterns (PAMPs) through membrane-bound pattern recognition receptors (PRRs) at the plant cell surface. Responses to PAMPs include a set of biochemical and transcriptional responses leading to the first inducible layer of defense called PAMP-triggered immunity (PTI).
To establish infection, pathogens must evade, suppress, or otherwise manipulate PTI. This is achieved by the secretion of proteins called effectors which act either outside or inside plant cells to target and perturb signaling, regulatory or mechanistic processes associated with defense. Effectors may themselves be targeted by a second layer of defense called effector-triggered immunity (ETI), since their presence inside or outside host cells may be detected by resistance proteins (R genes). ETI is stronger than PTI and often accompanied by localized programmed cell death (hypersensitive response (HR)) to counteract the pathogen. Effectors that are recognized by the R proteins are termed avirulence (AVR) proteins.

The intracellular oomycete effectors

The completion of the genome sequence of several Phytophthora species including P. infestans and P. sojae has led to the identification of a huge and, rapidly diverging superfamily of proteins, encoded by 100-700 genes per genome. Proteins in this family use the N-terminal motif RXLR-EER to cross the host plasma membrane. Once inside the cells, the so-called RXLR proteins are presumed to modulate host defense signaling for the benefit of the parasite, and are thus referred to as effectors.
Another effector family called Crinklers (for Crinkling and Necrosis ; CRN), has been also discovered in Phytophthora sp (> 200 genes). CRNs are modular proteins that comprise an N-terminal signal peptide, followed by a domain defined by the conserved but variable LXLFLAK motif involved in the translocation of CRN inside the host cell. The C-terminal domain is highly variable and is presumed to be involved in CRN function. So far, the function of CRN proteins is unknown.

The intracellular Aphanomyces euteiches CRN-effector family

Mining the 8 000 unigenes of AphanoDB (http://www.polebio.scsv.ups-tlse.fr...), revelead CRN genes, but not RXLR genes. A. euteiches CRNs harbour conserved N-termini comprising a LYLALK motif involved in the translocation inside the host cell. The C-terminal domain showed certain sequence similarities with various family members of P. infestans. The repertoire of CRN genes seems to be significantly smaller in A. euteiches compared to Phytophthora.

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Translocated CRN effectors
A). Schematic representation of AeCRN5 from A. euteiches. Numbers indicated amino acid position. B).Confocal imaging of GFP, GFP:PiCRN8, and GFP:AeCRN5 in N. benthamiana epidermal cells 24 h after infiltration. (Scale bars : 10 μm.) (Adapted from Schornack et al., PNAS, 2010 ; Gaulin et al., Plos One, 2008).

Main goal of our researches

Based on the oomycete phylogeny, our data support the view that CRN intracellular proteins arose early in oomycete evolution and diversified across plant pathogenic species. The main goal of our researches are to :

  • decipher the effector repertoire among Aphanomyces sp. by mining genomic data. Accordingly, A. euteiches strains are currently under sequencing (Genoscope-IBIsa_project and ANR Aphano-Effect) and RNAseq transcriptome are generated on various strains of Aphanomyces (plant, animal parasite species)
  • decipher the role of AeCRN proteins during A.euteiches/Medicago truncatula infection.