A protein associated with frost hardiness of western white pine is up-regulated by infection in the white pine blister rust pathosystem

A 19-kDa protein, Pin m III, was recently shown to be associated with overwintering and frost hardiness of western white pine (Pinus monticola Dougl. ex D. Don) seedlings. Here, we report that this protein is up-regulated by the fungus Cronartium ribicola Fisch, the causal agent of white pine blister rust in western white pine trees. Between 1991 and 1994, bark samples of mature western white pine trees (resistant with no stem cankers and susceptible with stem cankers) were collected in winter, spring, and fall. Proteins were extracted and analyzed by Western immunoblot utilizing specific rabbit polyclonal anti-Pin l I (a homologue of Pin m III) antibodies. During all collection dares, but particularly in the spring, susceptible trees had more Pin m m than resistant trees. In July 1995, 43 previously inoculated 7-year-old white pine seedlings were also analyzed. In all susceptible seedlings (cankered) tested, cankered tissue had high levels of Pin m m, and samples collected from the outside edge of the canker margin had low levels of Pin m III; this protein was also detected in some healthy bark of cankered trees. Since the level of Pin m III in healthy white pine trees is normally lowest in summer months, the high level Pin m III in summer samples of infected tissues is a consequence of the fungal infection.