Comparisons of pollen coat genes across Brassicaceae species reveal rapid evolution by repeat expansion and diversification
Comparisons of pollen coat genes across Brassicaceae species reveal rapid evolution by repeat expansion and diversification
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DOI：
10.1073/pnas.0305448101
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发表时间：
2004-03-02
影响因子：
11.1
通讯作者：
Preuss, D
中科院分区：
文献类型：
--
作者：
Fiebig, A;Kimport, R;Preuss, D
生殖基因和特征在许多生物体中迅速进化，包括软体动物、藻类和灵长类动物。以前，我们证明了一个家庭的富含甘氨酸的花粉表面蛋白（GRP）从拟南芥和甘蓝已经分歧很大，使同源基因的鉴定不可能，尽管只有2000万年的分离。在这里，我们解决这些变化背后的分子遗传机制，测序GRP簇的8个成员，沿着与11个相邻的基因在4个相关的物种，拟南芥arenosa，Olimarabidopsis pumila，荠菜rubella，和大蒜。我们发现，GRP基因比它们的邻居变化更快，它们更重复，并经历了更多的插入/缺失事件，同时保留重复的氨基酸组成。GRP簇侧翼的基因具有接近0.2的平均K-a/K-s，表明强纯化选择。这个比率在第一个GRP外显子中上升到大约0.5，表明放宽了选择性限制。第二GRP外显子的重复性质使得比对困难;即使如此，拟南芥属内的K-a/K-s表现出与外显子长度相关的增加。我们的结论是，快速GRP进化主要是由于重复序列的重复，缺失和分歧。GRP可能介导雌性细胞对花粉的识别和水合作用，这些基因的分歧可能与物种形成相关，甚至促进物种形成。我们测试了跨物种的相互作用，表明A。arenosa柱头水化花粉与GRP分歧相关，并鉴定A. arenosa作为一个模式，为未来的研究花粉识别。
Reproductive genes and traits evolve rapidly in many organisms, including mollusks, algae, and primates. Previously we demonstrated that a family of glycine-rich pollen surface proteins (GRPs) from Arabidopsis thaliana and Brassica oleracea had diverged substantially, making identification of homologous genes impossible despite a separation of only 20 million years. Here we address the molecular genetic mechanisms behind these changes, sequencing the eight members of the GRP cluster, along with 11 neighboring genes in four related species, Arabidopsis arenosa, Olimarabidopsis pumila, Capsella rubella, and Sisymbrium irio. We found that GRP genes change more rapidly than their neighbors; they are more repetitive and have undergone substantially more insertion/deletion events while preserving repeat amino acid composition. Genes flanking the GRP cluster had an average K-a/K-s approximate to 0.2, indicating strong purifying selection. This ratio rose to approximate to0.5 in the first GRP exon, indicating relaxed selective constraints. The repetitive nature of the second GRP exon makes alignment difficullt; even so, K-a/K-s within the Arabidopsis genus demonstrated an increase that correlated with exon length. We conclude that rapid GRP evolution is primarily due to duplication, deletion, and divergence of repetitive sequences. GRPs may mediate pollen recognition and hydration by female cells, and divergence of these genes could correlate with or even promote speciation. We tested cross-species interactions, showing that the ability of A. arenosa stigmas to hydrate pollen correlated with GRP divergence and identifying A. arenosa as a model for future studies of pollen recognition.