Identification of the pollen determinant of S-RNase-mediated self-incompatibility

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Many flowering plants have adopted self-incompatibility mechanisms to prevent inbreeding and promote out-crosses1. In the Solanaceae, Rosaceae and Scrophulariaceae, two separate genes at the highly polymorphic S-locus control self-incompatibility interactions: the S-RNase gene encodes the pistil determinant and the previously unidentified S-gene encodes the pollen determinant2,3,4. S-RNases interact with pollen S-allele products to inhibit the growth of self-pollen tubes in the style. Pollen-expressed F-box genes showing allelic sequence polymorphism have recently been identified near to the S-RNase gene in members of the Rosaceae and Scrophulariaceae5,6,7,8; but until now have not been directly shown to encode the pollen determinant. Here we report the identification and characterization of PiSLF, an S-locus F-box gene of Petunia inflata (Solanaceae). We show that transformation of S1S1, S1S2 and S2S3 plants with the S2-allele of PiSLF causes breakdown of their pollen function in self-incompatibility. This breakdown of pollen function is consistent with ‘competitive interaction’, in which pollen carrying two different pollen S-alleles fails to function in self-incompatibility1,9,10. We conclude that PiSLF encodes the pollen self-incompatibility determinant.

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Figure 1: Characterization of PiSLF.
Figure 2: Schematic representation of transformation experiments to ascertain the function of PiSLF.
Figure 3: Analyses of S1S1 transgenic plants carrying PiSLF2 transgene.
Figure 4: Analysis of progeny of an S2S3 transgenic plant, S2S3/PiSLF2-1, carrying a single copy of the PiSLF2 transgene.


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We thank A. H. Omeis for the greenhouse work, J. Wang for routine laboratory assistance and the Monsanto Sequencing Facility for sequencing the BAC clones. This work was supported by a Predoctoral Fellowship for Students with Disabilities from the National Institutes of Health (P.E.D.) and by grants from the National Science Foundation (T.-h.K.).

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Correspondence to Teh-hui Kao.

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The authors declare that they have no competing financial interests.

Supplementary information

Supplementary Figure S1

Alignment of the deduced amino acid sequences of three alleles of an S-locus F-box gene of Petunia inflata, named PiSLF. (JPG 184 kb)

Supplementary Figure S2

Schematic of the PiSLF2 construct used in all transformation experiments to generate transgenic plants expressing the PiSLF2 transgene. (JPG 20 kb)

Supplementary Figure Legends (DOC 19 kb)

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Sijacic, P., Wang, X., Skirpan, A. et al. Identification of the pollen determinant of S-RNase-mediated self-incompatibility. Nature 429, 302–305 (2004) doi:10.1038/nature02523

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