PURIFICATION, IMMUNOLOGICAL CHARACTERIZATION AND CDNA CLONING OF A 47-KDA GLYCOPROTEIN SECRETED BY CARROT SUSPENSION CELLS

A 47 kDa glycoprotein, termed EP4, was purified from carrot cell suspe nsion culture medium. An antiserum raised against EP4 also recognized a protein of 45 kDa that was ionically bound to the cell wall. EP4 was detected in culture media from both embryogenic and non-embryogenic c ell lines and was found to be secreted by a specific subset of non-emb ryogenic cells. Secretion of the 47 kDa glycoprotein by embryogenic ce lls was not evident. The 45 kDa cell wall-bound EP4 protein was specif ic for nonembryogenic cells and was shown by immunolocalization to occ ur in the walls of clustered cells, with the highest levels in the wal ls separating adjacent cells. In seedlings, EP4 proteins were mainly f ound in roots. EP4 cDNA was cloned by screening a cDNA library with an oligonucleotide derived from an EP4 peptide sequence. The EP4 cDNA se quence was found to be 55% homologous to ENOD8, an early nodulin gene from alfalfa.