Detection and seasonal expression pattern of a pathogenesis‐related protein (PR‐10) in Douglas‐fir (<i>Pseudotsuga menziesii</i>) tissues

Abstract

Previously, a PR‐10 protein Pin m III was described in western white pine. In this study, primers based on cDNA of Pin m III were utilized to obtain the genomic sequence of a Pin m III homologue – Pse m I – in Douglas‐fir. A comparative analysis of a deduced amino acid sequence of Pin m III and Pse m I genes indicated about 80% similarity between the two protein sequences, and a consensus 20 amino acid sequence located around the p‐loop sequence was used to synthesize a peptide of 20 amino acids. An antibody to this synthetic peptide was able to detect the Pse m I protein in Douglas‐fir. The anti‐ Pse m I antibody was used in a western immunoblot to monitor seasonal variation of the Pse m I in Douglas‐fir needles and its level was shown to increase with overwintering of Douglas‐fir seedlings. However, unlike the Pin m III, there is no indication that the Pse m I is associated with frost hardiness. Analysis of infected Douglas‐fir roots showed a possible trend to up‐regulation of Pse m I by pathogens such as the laminated root rot fungus, Phellinus weirii . The expression of Pse m I protein in Douglas‐fir seedlings is very low compared to the expression of Pin m III protein in western white pine seedlings. In addition, a light‐harvesting complex I protein, PSI‐F, was identified in Douglas‐fir by N‐terminal amino acid sequencing.