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 chara cterized from potato (Solanum tuberosum L.). A polymerase chain reacti on (PCR) probe was generated for the corresponding gene using oligonuc leotides based on internal peptide sequences of the protein, and the P CR probe was further employed to isolate cDNA and genomic clones. The sequence of the gene exhibits up to 70% similarity to previously descr ibed endochitinase class 1a protein sequences, and the purified protei n possesses chitinase {poly[1,4-(N-acetyl-beta-D-glucosaminide)] gluca nohydrolase, EC 3.2.1.14} activity. The protein, termed SK2, has been located by immunocytochemistry to the intercellular matrix of the styl ar transmitting tract. Immunoblot analysis has shown SK2 to be distinc t from the wound-induced chitinases of potato. The SK2-class of chitin ase is restricted in its distribution within the Solanaceae to the sub -family Solanoidae, which includes cultivated tomato and potato specie s. It was absent from the Cestroidae species tested (Petunia hybrida, Nicotiana tabacum). A role for SK2 endochitinase in protecting the ova ry against pollen-tube-mediated pathogen ingress is proposed.