HD-AGPs as Speciation Genes: Positive Selection on a Proline-Rich Domain in Non-Hybridizing Species of Petunia, Solanum, and Nicotiana

摘要: Transmitting tissue-specific proteins (TTS proteins) are abundant in the extracellular matrix of Nicotiana pistils, and vital for optimal pollen tube growth seed set. We have identified orthologs from several species Solanaceae, including Petunia axillaris integrifolia. refer to TTS their as histidine domain-arabinogalactan (HD-AGPs). HD-AGPs distinctive domains, a small histidine-rich region C-terminal PAC domain. Pairwise comparisons between 15 belonging Petunia, Nicotiana, Solanum show that his-domain domain under purifying selection. In contrast, proline-rich (HV2) is conserved among cross-hybridizing species, but variant species-pairs reproductively isolated by post-pollination pre-fertilization reproductive barriers. particular, variation tetrapeptide motif (XKPP) systematically correlated with presence an interspecific barrier. Ka/Ks ratios not informative at infrageneric level, reveal clear signature positive selection on two hypervariable domains (HV1 HV2) when five solanaceous genera compared. propose sequence divergence reinforces sympatric speciation incipient may first diverged consequence pollinator preferences or other ecological factors.