Hyaloperonospora arabidopsidis (Hpa) effector´s are able to suppress PTI in A. thaliana

GEORGINA FABRO; EVELYN KOERNER; DAVID STUDHOLME; JONATHAN D. G. JONES

Versailles, France

Simposio; 22nd New Phytologist Symposium Versailles 2009; 2009

Revista New Phytologist

We investigate how this obligate oomycete (Hpa) is able to manipulate its host, A. thaliana to establish a successful infection. We are characterizing Hpa effector proteins in collaboration with the ERAPG Hpa Effectoromics consortium. These effectors are small secreted proteins containing signal peptide and RxLR motifs. Through bioinformatic analysis of the Hpa Emoy2 race genome we identified ≈ 140 potential effectors of which 102 have been cloned. We tested if these effectors (69 now) are able to increase susceptibility in any of 12 A. thaliana ecotypes to the virulent bacteria Pseudomonas syringae (Pst) using a Heterologous (EDV) System (Sohn et al., Plant Cell 2007). We also analyzed if the effectors having a positive effect on plant susceptibility are able to suppress PTI, using the Pst ΔCEL strain and callose deposition suppression as a marker. We found that most of Hpa effectors are able to increase susceptibility to Pst. 87% of the Hpa RXLRs enhance Pst virulence on at least one accession, and 57% on at least 3 accessions. By the contrary, 66% of Hpa RXLRs decrease Pst virulence on at least one accession, 19.6% on 3 or more accessions. Also, 30% of the candidate RXLRs that enhance virulence do not decrease virulence on any Ecotype. These effectors can likely be targeting host Susceptibility Factors. There is also a positive correlation between enhanced susceptibility to the bacteria and callose deposition suppression by a given effector, i.e.: 78% of the Hpa effectors that could enhance bacterial growth in planta were also able to suppress at least 50% of the callose deposition triggered by Pst ΔCEL, indicating that PTI suppression might be a major mechanism for this pathogen to successfully invade its host. Only 18% of the tested effectors that do restrict bacterial growth are able to provoke HR-like lesions on the specific A.t. accessions that recognize them. When introduced in a non host species (Turnip) most of the effectors have no effect. Only 15% of the Hpa candidates seem to be recognized in a mild way and only 3% strongly, and 17% can enhance Turnip susceptibility to Pst.