Tracking type three effectors (T3E) rote in Ralstonia solanacearumleggplant interaction through functional and evolutionary approaches

Bacterial wilt caused by Ralstonia solanacearum is considered as one of the most harmful plant disease in the world1 due to its ability to infect more than 250 host plants2. Understanding the functions of type III effectors (TIE), which are major determinants of virulence, can contribute to the engineering of durable resistance in crops. This study attempted to identify genetic factors involved in virulence specificity to eggplant. We sequenced 10 putative effectors associated either to virulence/avirulence3 and/or to bacterium fitness4 on eggplant in 91 strains with different virulence profiles and geographical origin. Most conserved effectors are RipAJ (100% of strains) and RipEJ (97.S%), while RipP2 (67%), RipP 1 (69.1 %) and RipAX2 (S2.4%) are more variable. Distribution of TIEs was resolved in 11 profiles and 26 representative strains of these profiles were inoculated on resistant eggplant carrying the major resistant gene ERs15 (E6) and on susceptible (ES) eggplants in controlled conditions. TIE phylogenies compared to ''neutral" housekeeping genes phylogenies showed incongruences for three TIE (among five analyzed) suggesting recombination events. Defective mutants of each of the 10 TIE in the GMIIOOO strain were also tested on E6 and ES. GMI1OOO strain defective in RipAX2 induced wilting of resistant eggplant by root inoculation, thus indicating its involvement in the control of GMIlOOO by E6 and a potential gene-for-gene interaction. While we failed to detect HR with agro-clone carrying RipAX2GMI1ooo, IGC data showed that the control of the bacteria happen at the basis of the stem, suggesting that E6 resistance is organ specific. These results indicate that RipAX2 is an avirulent factor on resistant eggplant (E6). Further studies will investigate the functional diversity ofRipAX2 in R.solanacearum strains. (Resume d'auteur)