During the past several years we have been involved in identifying seasonally regulated proteins and genes from peach bark. In the present study, we describe the cloning of a protease inhibitor from a cDNA library made from winter bark tissues. A partial clone obtained from the library was extended to full length by 5' RACE. The full-length cDNA clone (final3b) is 613 bp in length, not including the poly A+ tail. The open reading frame of 237 bp codes for a 79 amino acid protease inhibitor related to the defensin family of proteins. This family of small, cysteine-rich, extracellular proteins play a role in the plantís defense response through their antifungal properties. Sequence comparison of the encoded protein using BLAST analysis revealed significant homology to protease inhibitors from Glycine max, Arabidopsis thaliana, and a defensin protein from bell pepper (Capsicum annuum). Similar to these other cysteine-rich proteins, the peach defensin contains a consensus cys arrangement and is predicted to have an amino terminal signal peptide, presumably targeting it for extracellular transport. RNA-blot analysis indicated that the gene is seasonally expressed in bark tissues of 1-year-old shoots. Transcript abundance of final3b increased in the fall, reached a peak in midwinter and then decreased. The gene was also expressed during early stages of fruit development. RNA-blot analysis of the gene in other tissues, and in response to environmental stress and wounding, is in progress.
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