Cellulose Binding Domains of a Phytophthora Cell Wall Protein Are Novel Pathogen-Associated Molecular Patterns

Abstract

The cellulose binding elicitor lectin (CBEL) from Phytophthora parasitica nicotianae contains two cellulose binding domains (CBDs) belonging to the Carbohydrate Binding Module1 family, which is found almost exclusively in fungi. The mechanism by which CBEL is perceived by the host plant remains unknown. The role of CBDs in eliciting activity was investigated using modified versions of the protein produced in Escherichia coli or synthesized in planta through the potato virus X expression system. Recombinant CBEL produced by E. coli elicited necrotic lesions and defense gene expression when injected into tobacco (Nicotiana tabacum) leaves. CBEL production in planta induced necrosis. Site-directed mutagenesis on aromatic amino acid residues located within the CBDs as well as leaf infiltration assays using mutated and truncated recombinant proteins confirmed the importance of intact CBDs to induce defense responses. Tobacco and Arabidopsis thaliana leaf infiltration assays using synthetic peptides showed that the CBDs of CBEL are essential and sufficient to stimulate defense responses. Moreover, CBEL elicits a transient variation of cytosolic calcium levels in tobacco cells but not in protoplasts. These results define CBDs as a novel class of molecular patterns in oomycetes that are targeted by the innate immune system of plants and might act through interaction with the cell wall.

The Downy Mildew Effector Proteins ATR1 and ATR13 Promote Disease Susceptibility in Arabidopsis thaliana

“…These results were surprising because Pst DC3000, which carries >30 effector proteins, is already a highly virulent bacterial pathogen Buell et al, 2003). Moreover, ATR13-mediated suppression of callose deposition at Arabidopsis cell walls suggests that ATR13 may play a role in suppressing PTI activated by oomycete elicitors such as Nep1-like proteins or CBEL (Gaulin et al, 2006;Qutob et al, 2006). ATR13-mediated callose suppression is the first indication to date of the suppression of host PTI by an oomycete effector, and this suggests that the molecular functions of bacterial and oomycete effectors can overlap.…”

Necrotroph Attacks on Plants: Wanton Destruction or Covert Extortion?

“…The Phytophthora cellulose binding elicitor lectin (CBEL) protein is a P/MAMP that is a potent inducer of innate immune responses (Khatib et al, 2004;Gaulin et al, 2006). CBEL is a cell wall glycoprotein from Phytophthora parasitica var nicotianae (Ppn), the causal agent of the black shank disease of tobacco.…”

“…CBEL is a cell wall glycoprotein from Phytophthora parasitica var nicotianae (Ppn), the causal agent of the black shank disease of tobacco. This glycoprotein is widely conserved in the genus Phytophthora and elicits HR-like lesions, defense responses, and protection against subsequent infection with this oomycete in host tobacco and non-host Arabidopsis plants (Khatib et al, 2004;Gaulin et al, 2006). Interestingly, the cellulose binding domain (CBD) of CBEL is essential and suffi cient to induce immune responses.…”

A Phytophthora sojae Glycoside Hydrolase 12 Protein Is a Major Virulence Factor during Soybean Infection and Is Recognized as a PAMP

“…Plants can recognize many different PAMPs from bacteria and fungi (Newman et al, 2013). PAMPs identified so far from oomycetes include b-glucans, heptaglucoside, transglutaminase (Pep13), cellulose binding elicitor lectins, and elicitins (Sharp et al, 1984;Yu, 1995;Enkerli et al, 1999;Klarzynski et al, 2000;Brunner et al, 2002;Gaulin et al, 2006;Zhang et al, 2014). Nevertheless, the mechanisms that allow plants to perceive oomycetes as non-self and to defend against infection remain only partly known.…”