Analysis of bark proteins in blister rust-resistant and susceptible western white pine (Pinus monticola)

We compared bark proteins from four contrasting (blister rust-resistant versus susceptible) half-sib seedling pairs of western white pine (Pinus monticola D. Don). Pooled proteins from resistant and susceptible groups (four trees per group) were separated by two-dimensional gel electrophoresis, silver stained, and analyzed with the aid of a laser scanner interfaced with a computerized gel documentation system. Qualitative and quantitative protein differences were observed between resistant and susceptible groups. The number of proteins unique to a group was greater in the susceptible category than in the resistant category. Biosynthesis of some common proteins was enhanced near lesioned areas of susceptible seedlings. Many proteins shared similar charge and mass characteristics with those of pathogenesis-related (PR) proteins. Two protein bands were isolated and partially characterized by N-terminal amino acid sequencing: a 10.6-kDa band that was selectively enriched in all resistant individuals, and a 26.0-kDa band that was enriched in some susceptible individuals. The significance of these protein differences and the possible use of selected proteins as disease or resistance markers are discussed.