MOLECULAR CHARACTERIZATION OF A REPRODUCTIVE ORGAN-SPECIFIC CDNA CLONE, ISP11 FROM IPOMOEA-TRIFIDA

A cDNA clone, ISP11, that exhibits a specific expression in the stigma and pollen has been isolated from a cDNA library constructed for poly (A)(+) RNA from mature stigma of Ipomoea trifida. The cDNA with a leng th of 1037 nucleotides excluding poly(A) tail codes for a predicted po lypeptide containing 201 amino acid residues and with a molecular mass of 22.8 kilodaltons. The hydropathy profile suggests that the polypep tide is a water-soluble protein without a signal sequence on the amino terminus. A computer search of sequence database failed to reveal any significant homologies with known molecules. RNA gel blot analysis sh owed that gene expression of ISP11 was developmentally regulated along with the progress in flower bud growth. Southern hybridizations of ge nomic DNA to ISP11 probe indicated that the ISP11 gene is present as a single copy in the haploid genome and is not linked to the self-incom patibility locus. These facts suggest that the ISP11 protein plays a g eneral role in pollen germination and/or the resulting process of fert ilization, rather than in self-recognition associated with the self-in compatibility of I. trifida.