Characterization of Pin m III cDNA in western white pine.

Maximum accumulation of Pin m III protein in western white pine (Pinus monticola Dougl. ex D. Don) needles occurred during the winter months. To characterize Pin m III, an expression cDNA library from poly(A)+ mRNA of needles was immunoscreened and the full length cDNA was cloned. An open reading frame of 486 bases encodes a protein of 161 amino acid residues with a molecular mass of 18 kD and a predicted isoelectric point of 5.5. The deduced amino acid sequence had some similarities (37%) with an intracellular pathogenesis-related (PR) protein from garden asparagus (Asparagus officinalis L.) and the major pollen allergen from white birch (Betula verrucosa J. F. Ehrh.), which are members of the ribonuclease-like PR-10 family. Phylogenetic analysis provided circumstantial evidence that Pin m III may be grouped with intracellular PRs from asparagus and potato (Solanum tuberosum L.), while the allergens formed another subgroup. Northern analysis showed that the Pin m III gene was preferentially expressed during cold acclimation with the highest expression in the fall and winter months, preceding the peak of Pin m III protein accumulation. Tissue specificity expression analysis indicated that the gene was strongly expressed in roots and twigs. Higher amounts of the homologous protein (Pin l I) and its transcript accumulated in sugar pine (Pinus lambertiana Dougl.) needles infected with blister rust compared with healthy needles.