Mapping genes for resistance to bacterial blight (Pseudomonas syringae pv. pisi) in pea and identification of genes involved in resistance by DeepsuperSAGE transcriptome profiling

Bacterial blight caused by Pseudomonas syringae pv. pisi is an important disease of pea (Pisum sativum L.). Knowledge about the genes or mechanisms acting against this pathogen is scarce. A genetic mapping study of the resistance was performed using a recombinant inbred line mapping population generated by crossing the susceptible cultivar Cheyenne to the resistant line ZP0104. Resistance to race 2 was a dominant monogenic trait mapped at 109.4 cM on LGVII between AB114 and AB122 simple sequence repeat markers. It is assumed to be the previously Ppi2 based on its location. Resistance to races 4 and 8 behaved also as dominant monogenic traits and presumably due to a single gene conferring resistance to both races. It was mapped on LGIII at 11.2 cM of the AD57 microsatellite marker. This gene has been named Ppi8 and it is proposed as a new resistance gene. Ppi8 and Ppi2 are associated to the pea consensus map for the first time. To identify genes related to resistance and susceptibility, a DeepSuperSAGE genome-wide transcription profiling approach was conducted producing 45,261 different pea unitags. A set of 651 unitags were differently represented in the susceptible versus the resistant response with a significance of P < 0.001 and a fold change >4. These putative differentially expressed set includes genes previously related to responses to biotic stresses (pathogenesis-related or related to disease resistance responses), abiotic stresses or of unknown function, among other.