The most abundant soluble basic protein of the stylar transmitting tract in potato (Solanum tuberosum L.) is an endochitinase

An abundant, pistil-specific basic protein has been purified and characterized from potato (Solanum tuberosum L.). A polymerase chain reaction (PCR) probe was generated for the corresponding gene using oligonucleotides based on internal peptide sequences of the protein, and the PCR probe was further employed to isolate cDNA and genomic clones. The sequence of the gene exhibits up to 70% similarity to previously described endochitinase class 1a protein sequences, and the purified protein possesses chitinase {poly[1, 4-(N-acetyl--D-glucosaminide)] glucanohydrolase, EC 3.2.1.14} activity. The protein, termed SK2, has been located by immunocytochemistry to the intercellular matrix of the stylar transmitting tract. Immunoblot analysis has shown SK2 to be distinct from the wound-induced chitinases of potato. The SK2-class of chitinase is restricted in its distribution within the Solanaceae to the sub-family Solanoidae, which includes cultivated tomato and potato species. It was absent from the Cestroidae species tested (Petunia hybrida, Nicotiana tabacum). A role for SK2 endochitinase in protecting the ovary against pollen-tubemediated pathogen ingress is proposed.Abbreviations FPLC fast protein liquid chromatography - IEF isoelectric focussing - PCR polymerase chain reactionWe are indebted to Drs. E. Kombrink, J. Logemann, J. Schmidt and Mr. G. Jach (MPI für Züchtungsforschung, Köln, Germany) for advice on chitinase assays. The technical assistance of Ms. U. Seul and Mrs. B. Piegeler is gratefully acknowledged. Electron microscopy was carried out under the supervision of Drs. Brian Wells and Keith Roberts, (John Innes Centre for Plant Science Research, Norwich, UK). This research was supported by the Deutsche Forschungsgemeinschaft SPP Mechanisms of Hybrid Breeding, and the EC BRIDGE programme.