Molecular Basis of Gametophytic Self-Incompatibility in Nicotiana and Petunia

The proposed project is to study the functional aspects of pistil S-proteins and regulation of S-gene expression in gametophytic self-incompatibility. Using Nicotiana alata and Petunia inflata, Dr. Kao will 1) establish direct evidence that S-proteins are responsible for the self-incompatibility reaction by testing the effect on self-incompatibility behavior of introducing either a new S-gene into plants homozygous for a different S-allele, or an antisense S-gene into plants homozygous for the same S-allele; 2) identify the s-allele specificity domain of the S-protein by using chimeric S-proteins expressed in transgenic plants; 3) test the effect of mutating the conserved cysteine residues of S- proteins on their function; 4) determine the sequences controlling tissue specific and developmentally regulated expression of S-genes by fusing their 5' upstream sequences to a reporter gene, GUS, and then using sequential deletion to test the effect on expression of GUS in transgenic plants; 5) identify a protein associated with the style activity part of the S-locus using a unique self-compatible style-part mutant of N. alata. The result of these experiment will yield important information on the molecular basis of self-incompatibility. %%% Many higher plants have a mechanism, termed self-incompatibility, with prevents the pollen from a given plant from self fertilizing the female tissue (pistil) of the same plant. Genes controlling this self- incompatibility have been identified but the mechanism whereby the incompatibility occurs is unknown. In addition to its inherent interest to plant biologists, there are clear applications to agriculture to an understanding of this process.