Analysis of wound-induced transcripts in poplar leaf disks versus whole leaves

Expression of defense response-related transcripts could be affected upon leaf wounding such as after excision of leaf disks. In this experiment, transcripts were isolated from whole leaves and 5-cm2 excised leaf disks samples from interaction assays between leaves of the 'Beaupré' poplar cultivar (Poplus trichocarpa x Poplus deltoides) and virulent (98AG31, compatible interaction) and avirulent (93ID6, incompatible interaction) urediniospores of Melampsora larici-populina, the fungus responsible for the foliar rust disease in poplar. For each type of interaction, three samples were collected in a time-course series (18, 21 and 24 hpi for strain 93ID6, and 18, 24 and 48 hpi for strain 98AG31). Both leaf disks and whole leaves were inoculated in strictly similar conditions, so differential transcript expression is likely attributable to the wounding effect in leaf disks. The aim of this study is to identify genes that are induced by wounding in leaf disks compared with whole leaves. For this purpose, cDNA templates were used for hybridization on poplar oligoarrays. We performed 12 hybridizations (NimbleGen oligoarrays) with samples derived from incompatible (18, 21 and 24hpi) and compatible (18, 24 and 48hpi) interactions of Melampsora larici-populina with P. trichocarpa x P. deltoides poplar cultivar 'Beaupré' leaf disks (6 conditions) and whole leaves (6 conditions). All samples were labeled with Cy3.