Genetic features of a pollen-part mutation suggest an inhibitory role for the Antirrhinum pollen self-incompatibility determinant
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Self-incompatibility (SI), an important barrier to inbreeding in flowering plants, is controlled in many species by a single polymorphic S-locus. In the Solanaceae, two tightly linked S-locus genes, S-RNase and SLF (S-locus F-box)/SFB (S-haplotype-specific F-box), control SI expression in pistil and pollen, respectively. The pollen S-determinant appears to function to inhibit all but self S-RNase in the Solanaceae, but its genetic function in the closely-related Plantaginaceae remains equivocal. We have employed transposon mutagenesis in a member of the Plantaginaceae (Antirrhinum) to generate a pollen-part SI-breakdown mutant Pma1 (Pollen-part mutation in Antirrhinum1). Molecular genetic analyses showed that an extra telocentric chromosome containing AhSLF-S 1 is present in its self-compatible but not in its SI progeny. Furthermore, analysis of the effects of selection revealed positive selection acting on both SLFs and SFBs, but with a stronger purifying selection on SLFs. Taken together, our results suggest an inhibitor role of the pollen S in the Plantaginaceae (as represented by Antirrhinum), similar to that found in the Solanaceae. The implication of these findings is discussed in the context of S-locus evolution in flowering plants.
KeywordsSelf-incompatibility Antirrhinum SLF Pollen-part mutation S-RNase
We thank Enrico Coen and Rosemary Carpenter for providing Antirrhinum plants and constant support and advice, Peter Walker for growing the plants and Ruth McGrath, Gwyneth Ingram and Richard Waites for their involvement in the mutagenesis work. This work was supported by the Ministry of Science and Technology of China (2007CB947603) to Y. Xue and the UK Biotechnology and Biological Sciences Research Council to H.D.
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