雅芳峡谷花楸的繁殖系统、杂交和持续进化。
Breeding systems, hybridization and continuing evolution in Avon Gorge Sorbus.
机构信息
School of Biological Sciences, University of Bristol, Bristol, UK.
出版信息
Ann Bot. 2013 Apr;111(4):563-75. doi: 10.1093/aob/mct013. Epub 2013 Feb 13.
BACKGROUND AND AIMS
Interspecific hybridization and polyploidy are key processes in plant evolution and are responsible for ongoing genetic diversification in the genus Sorbus (Rosaceae). The Avon Gorge, Bristol, UK, is a world 'hotspot' for Sorbus diversity and home to diploid sexual species and polyploid apomictic species. This research investigated how mating system variation, hybridization and polyploidy interact to generate this biological diversity.
METHODS
Mating systems of diploid, triploid and tetraploid Sorbus taxa were analysed using pollen tube growth and seed set assays from controlled pollinations, and parent-offspring genotyping of progeny from open and manual pollinations.
KEY RESULTS
Diploid Sorbus are outcrossing and self-incompatible (SI). Triploid taxa are pseudogamous apomicts and genetically invariable, but because they also display self-incompatibility, apomictic seed set requires pollen from other Sorbus taxa - a phenomenon which offers direct opportunities for hybridization. In contrast tetraploid taxa are pseudogamous but self-compatible, so do not have the same obligate requirement for intertaxon pollination.
CONCLUSIONS
The mating inter-relationships among Avon Gorge Sorbus taxa are complex and are the driving force for hybridization and ongoing genetic diversification. In particular, the presence of self-incompatibility in triploid pseudogamous apomicts imposes a requirement for interspecific cross-pollination, thereby facilitating continuing diversification and evolution through rare sexual hybridization events. This is the first report of naturally occurring pseudogamous apomictic SI plant populations, and we suggest that interspecific pollination, in combination with a relaxed endosperm balance requirement, is the most likely route to the persistence of these populations. We propose that Avon Gorge Sorbus represents a model system for studying the establishment and persistence of SI apomicts in natural populations.
背景与目的
种间杂交和多倍体化是植物进化的关键过程，也是蔷薇科苹果属（Sorbus）持续遗传多样化的原因。英国布里斯托尔的埃文峡谷是苹果属多样性的世界“热点”，这里有二倍体有性物种和多倍体无融合生殖物种。本研究调查了交配系统的变异、杂交和多倍体化如何相互作用产生这种生物多样性。
方法
通过控制授粉的花粉管生长和结实试验，以及开放授粉和人工授粉后代的亲子基因型分析，研究了二倍体、三倍体和四倍体苹果属分类群的交配系统。
主要结果
二倍体苹果属是异交和自交不亲和（SI）的。三倍体类群是假配子无融合生殖的，遗传上是不变的，但由于它们也表现出自交不亲和性，无融合生殖种子的形成需要来自其他苹果属分类群的花粉——这一现象提供了直接杂交的机会。相比之下，四倍体类群是假配子自交亲和的，因此不需要同种间授粉的强制性要求。
结论
埃文峡谷苹果属分类群之间的交配相互关系是复杂的，是杂交和持续遗传多样化的驱动力。特别是，三倍体假配子无融合生殖的自交不亲和性要求种间异花授粉，从而通过罕见的有性杂交事件促进持续的多样化和进化。这是首例自然发生的假配子无融合生殖 SI 植物种群的报告，我们认为种间授粉与松弛的胚乳平衡要求相结合，是这些种群持续存在的最可能途径。我们提出，埃文峡谷苹果属代表了一个研究自然种群中 SI 无融合生殖建立和持续存在的模型系统。
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