cDNA cloning, structure, and expression of a novel pathogenesis-related protein in bean

We have isolated cDNA clones spanning the full length of a transcript (PvPR3) encoding a novel pathogenesis-related (PR) protein in bean (Phaseolus vulgaris). The PvPR3 transcript accumulates gradually over 24 hr in elicitor-treated cell suspensions. This pattern of expression is distinct from those of previously reported elicitor-induced transcripts in bean. Specifically, transcripts encoding two recently described acidic bean PR proteins, phenylpropanoid pathway enzymes, accumulate to maximal levels by 4-8 hr, while hydroxyproline-rich glycoprotein mRNA accumulation is delayed by several hours. The PvPR3 mRNA also accumulates after wounding of hypocotyls with kinetics comparable to those of mRNA encoding phenylpropanoid pathway mRNAs. PvPR3 appears to exist as a single gene within a family of approximately 15 related genes in the bean genome. The PvPR3 protein deduced from the cDNA sequences (14,950 Da pI = 10.0) lacks a putative signal peptide suggesting a cytosolic localization. Amino acid sequence comparisons with databases revealed that PvPR3 represents a new class of PR proteins without significant sequence homology to previously characterized PR proteins or other proteins.