Identification and characterization of an mRNA encoding a proline-rich protein that rapidly declines in abundance in the tips of harvested asparagus spears.

We previously isolated a cDNA clone, pTIP13, whose homologous mRNA rapidly declined in abundance in the tips of harvested asparagus (Asparagus officinalis L.) spears [King and Davies (1992) Plant Physiol. 100: 1661]. In order to identify factors regulating the postharvest deterioration of asparagus, we have now sequenced the pTIP13 cDNA, derived the encoded amino acid sequence and determined the cellular location of pTIP13 mRNA by in situ hybridization. pTIP13 encodes a derived protein that is rich in proline (22.3%), but also has a high content of lysine (15.2%) and threonine (14.1%). The proline residues are located in motifs at the amino-terminal region of the protein. The carboxyl-terminal region of the derived protein has a high leucine content and shares > 64% amino acid identity with derived proteins identified from cDNA clones to cell wall protein precursor mRNAs obtained from soybean hypocotyls, alfalfa roots, and tomato fruit. Genomic Southern analysis suggests that pTIP13 is encoded by a single-copy gene in asparagus. pTIP13 mRNA was localized to specific cell types in the young bracts of the asparagus spear tip. The results provide new information on the complexity of tissue responses in the tips of asparagus spears following harvest.