Expression analysis of ROS scavenging enzyme encoding genes in rubber tree infected by Microcyclus ulei

South American Leaf Blight (SALB), caused by the ascomycete Microcyclus ulei is responsible for the low productivity of rubber tree in Latin America and represents an important threat for rubber plantations in Asia and Africa, where production is derived from highly susceptible clones. In order to identify candidate genes involved in the resistance, an unigene set of 1623 ESTs were obtained from five SSH libraries. Arrays analyses were performed to identify genes differentially expressed in resistant and susceptible cultivars. Fourteen genes were selected for further gene expression analysis in three non-inoculated and inoculated genotypes: FX2784 (HR), MDF180 (partially resistant) and PB314 (susceptible) from 24 to 216 hpi. These genes are involved in ROS-scavenging systems (HbCuZnSOD, HbMnSOD, HbCat, HbAPX1, HbAPX2, HbMDHAR, HbGCL1, HbGCL2, HbOASTL) and leaf senescence (HbCASP, HbPCYST, HbWRKY2, HbPLY, HbKAT2). Six genes were differentially expressed in the different genotypes and/or during the infection. The average basal levels of HbCat, HbGCL1 and 2 expressions in MDF180 were respectively 55-fold and 2- to 3-fold lower than in the other genotypes. HbPCYST was both up-regulated 216 hpi in inoculated and non-inoculated MDF180 tissues. HbWRKY2 was up-regulated in inoculated leaves of MDF180 at 216 hpi while in PB314, the up-regulation started at 96 hpi with a peak of expression at 168 hpi. HbPLY was up-regulated in PB314 inoculated tissue at 168 hpi while in MDF180 and FX2784 a down-regulation was observed in inoculated tissues. The results were compared with histological observations. These genes can be considered as reporter genes of the oxidative status and senescence of the leaf during the infection. (Resume d'auteur)