Research Article

Collaborative Non-Self Recognition System in S-RNase–Based Self-Incompatibility

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Science  05 Nov 2010:
Vol. 330, Issue 6005, pp. 796-799
DOI: 10.1126/science.1195243

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Dissecting Self-Incompatibility

Although the pollen may be available for a flower to fertilize itself, molecular determinants on the pollen and the pistil prevent inbreeding in a process termed self-incompatibility. In the Petunia self-incompatibility, if male determinants (F-box proteins) on pollen are recognized by a female ribonuclease determinant on the pistil, the pollen tube is killed when its ribosomal RNA is digested. Outcrossed fertilizations can occur because of allelic diversity in the female that fails to recognize its male counterparts; however, the genetic diversity of the ribonuclease gene is greater than that of the known F-box gene. Kubo et al. (p. 796; see the Perspective by Indriolo and Goring) have discovered that there are several related F-box genes in Petunia, each of which brings its own allelic diversity to bear—thus, increasing the variety of potential mating partners.

Abstract

Self-incompatibility in flowering plants prevents inbreeding and promotes outcrossing to generate genetic diversity. In Solanaceae, a multiallelic gene, S-locus F-box (SLF), was previously shown to encode the pollen determinant in self-incompatibility. It was postulated that an SLF allelic product specifically detoxifies its non-self S-ribonucleases (S-RNases), allelic products of the pistil determinant, inside pollen tubes via the ubiquitin–26S-proteasome system, thereby allowing compatible pollinations. However, it remained puzzling how SLF, with much lower allelic sequence diversity than S-RNase, might have the capacity to recognize a large repertoire of non-self S-RNases. We used in vivo functional assays and protein interaction assays to show that in Petunia, at least three types of divergent SLF proteins function as the pollen determinant, each recognizing a subset of non-self S-RNases. Our findings reveal a collaborative non-self recognition system in plants.

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