Molecular analysis of gene-products associated with self-incompatibility in Ipomoea trifida

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The present study was performed to reveal stigma proteins associated with self-incompatibility in a wild relative of the sweet potato, Ipomoea trifida. A cDNA clone, IRK1 isolated from stigama cDNA library of I.trifida was found to encode SLG/SRK-like proteins that have been identified as self-incompatibility gene (S-gene) products in Brassica. RFLP analysis of F1 population segregating for S-alleles, however, showed that the IRK1 gene is genetically unlinked to the S-locus. S-RNases have been shown to be involved in self-incompatibility reaction of solanaceous plants. An RNase cDNA clone, IRN3 isolated from stigma cDNA library of I.trifida, also showed no linkage to the S-locus. These results suggest that Ipomoea plants possessaself-incompatibility mechanism different from those of Brassica and solanaceous plants. In the present study, stigma extracts obtained from six S-allele homozygotes were analyzed by two-dimensional electrophoresis. From comparison of electrophoretic patterns among the homozygotes, we have identified the protein spots specific for S-alleles. These S-allele specific proteins have a range of molecular mass of 60-80 kD with acidic to neutral PI.Co-segregation of these proteins with S-genotypes was confirmed in heterozygous plants for S-alleles. Further studies on the structure and function of these protein are now conducted through getting the data on the N-terminal amino acid sequence and screening of full cDNA clone from the stigma cDNA library.