IDENTIFICATION AND CHARACTERIZATION OF AN MESSENGER-RNA 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 rap idly declined in abundance in the tips of harvested asparagus (Asparag us officinalis L.) spears [King and Davies (1992) Plant Physiol. 100: 1661]. In order to identify factors regulating the postharvest deterio ration of asparagus, we have now sequenced the pTIP13 cDNA, derived th e 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 lysin e (15.2%) and threonine (14.1%). The proline residues are located in m otifs at the amino-terminal region of the protein. The carboxyl-termin al region of the derived protein has a high leucine content and shares >64% amino acid identity with derived proteins identified from cDNA c lones to cell wall protein precursor mRNAs obtained from soybean hypoc otyls, alfalfa roots, and tomato fruit. Genomic Southern analysis sugg ests 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 comple xity of tissue responses in the tips of asparagus spears following har vest.