Genetic analysis of Nicotiana pollen-part mutants is consistent with the presence of an S-ribonuclease inhibitor at the S locus.
Self-incompatibility (SI) is a genetic mechanism that restricts inbreeding in flowering plants. In the nightshade family (Solanaceae) SI is controlled by a single multiallelic S locus. Pollen rejection in this system requires the interaction of two S locus products: a stylar (S)-RNase and its pollen counterpart (pollen S). pollen S has not yet been cloned. Our understanding of how this gene functions comes from studies of plants with mutations that affect the pollen but not the stylar SI response (pollen-part mutations). These mutations are frequently associated with duplicated S alleles, but the absence of an obvious additional allele in some plants suggests pollen S can also be deleted. We studied Nicotiana alata plants with an additional S allele and show that duplication causes a pollen-part mutation in several different genetic backgrounds. Inheritance of the duplication was consistent with a competitive interaction model in which any two nonmatching S alleles cause a breakdown of SI when present in the same pollen grain. We also examined plants with presumed deletions of pollen S and found that they instead have duplications that included pollen S but not the S-RNase gene. This finding is consistent with a bipartite structure for the S locus. The absence of pollen S deletions in this study and perhaps other studies suggests that pollen S might be required for pollen viability, possibly because its product acts as an S-RNase inhibitor.
Golz
J F
JF
Plant Cell Biology Research Centre, School of Botany, University of Melbourne, Victoria 3010, Australia.
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Kusaba
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Newbigin
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D000483:Alleles; D006023:Glycoproteins / Q000235:genetics*; D017404:In Situ Hybridization, Fluorescence; D008969:Molecular Sequence Data; D009154:Mutation; D010940:Plant Proteins / Q000235:genetics*; D011058:Pollen / Q000235:genetics*; D012260:Ribonucleases / Q000037:antagonists & inhibitors*; D014026:Nicotiana / Q000235:genetics*
D006023:Glycoproteins; D010940:Plant Proteins; C076697:self-incompatibility glycoprotein, Nicotiana; D012260:Ribonucleases