Molecular Basis of Self-Incompatibility in Petunia

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IBN-9982659PI: Teh-hui KaoPetunia inflata possesses gametophytic type self-incompatibility which iscontrolled by a polymorphic locus, the S-locus. Matching of S-allelescarried by the pollen and pistil results in inhibition of pollen tubegrowth in the style. A polymorphic gene at the S-locus, termed the S-RNasegene, that controls pistil function in SI has been identified. However, thegene that controls pollen function in SI interactions, termed the pollenS-gene, has not been identified.The goal of this proposed project is to use a functional genomic approachto identify the pollen S-gene of P. inflata. Obj. I is to use 14 cDNAmarkers for the S-locus and the S-RNase gene as probes to isolate clonesfrom an S2S2 BAC library already contsructed. Obj. II is to construct a BAClibrary of the S1S1 genotype and use the same probes employed in Obj. I toisolate positive clones. Obj. III is to characterize all the BAC clonesisolated in Obj. I and II by pulse-field gel electrophoresis andfluorescence in situ hybridization to determine any overlap between them,to order them at the S-locus, and to estimate the size of the gaps betweenthem. Additional clones will be isolated from both BAC libraries to coveras extensively as possible the entire S-locus. Obj. IV is to introduce allthe BAC clones separately into P. inflata plants of S1S2 genotype todetermine whether any of them contains the pollen S-gene. If a BAC clonecontains the pollen S2-gene, a quarter of the pollen grains produced by atransgenic plant will carry the pollen S1-allele and the pollenS2-transgene, and they will be compatible with S1S2 pistils due tocompetitive interaction. Transgenic plants that have becomeself-compatible will be studied to identify the transgene that isresponsible for the phenotype. The function of the candidate(s) for thepollen S-gene will be further ascertained by loss-of-function experiments.Accomplishment of this proposed research will advance the understanding ofan RNase-based self/non-self recognition mechanism. The BAC clones isolatedcan be used for studying the functions of additional S-locus genes, and forcomparative 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 SItrait to self-compatible cultivated species to facilitate hybrid seedproduction. If successful, this will have a very important agronomicimpact.