Molecular Basis of Self-Incompatibility in Petunia

IBN-9982659 PI: Teh-hui Kao Petunia inflata possesses gametophytic type self-incompatibility which is controlled by a polymorphic locus, the S-locus. Matching of S-alleles carried by the pollen and pistil results in inhibition of pollen tube growth in the style. A polymorphic gene at the S-locus, termed the S-RNase gene, that controls pistil function in SI has been identified. However, the gene that controls pollen function in SI interactions, termed the pollen S-gene, has not been identified. The goal of this proposed project is to use a functional genomic approach to identify the pollen S-gene of P. inflata. Obj. I is to use 14 cDNA markers for the S-locus and the S-RNase gene as probes to isolate clones from an S2S2 BAC library already contsructed. Obj. II is to construct a BAC library of the S1S1 genotype and use the same probes employed in Obj. I to isolate positive clones. Obj. III is to characterize all the BAC clones isolated in Obj. I and II by pulse-field gel electrophoresis and fluorescence in situ hybridization to determine any overlap between them, to order them at the S-locus, and to estimate the size of the gaps between them. Additional clones will be isolated from both BAC libraries to cover as extensively as possible the entire S-locus. Obj. IV is to introduce all the BAC clones separately into P. inflata plants of S1S2 genotype to determine whether any of them contains the pollen S-gene. If a BAC clone contains the pollen S2-gene, a quarter of the pollen grains produced by a transgenic plant will carry the pollen S1-allele and the pollen S2-transgene, and they will be compatible with S1S2 pistils due to competitive interaction. Transgenic plants that have become self-compatible will be studied to identify the transgene that is responsible for the phenotype. The function of the candidate(s) for the pollen S-gene will be further ascertained by loss-of-function experiments. Accomplishment of this proposed research will advance the understanding of an RNase-based self/non-self recognition mechanism. The BAC clones isolated can be used for studying the functions of additional S-locus genes, and for comparative study of the S-locus of two different S-haplotypes, S1 and S2. On the practical side, one can explore the possibility of restoring the SI trait to self-compatible cultivated species to facilitate hybrid seed production. If successful, this will have a very important agronomic impact.