背景回顾：Supergenes govern multi-trait-balanced polymorphisms in a wide range of systems; however, our understanding of their origins and evolution remains incomplete. The reciprocal placement of stigmas and anthers in pin and thrum floral morphs of distylous species constitutes an iconic example of a balanced polymorphism governed by a supergene, the distyly S-locus. 

提出问题：Recent studies have shown that the Primula and Turnera distyly supergenes are both hemizygous in thrums, but it remains unknown whether hemizygosity is pervasive among distyly S-loci. As hemizygosity has major consequences for supergene evolution and loss, clarifying whether this genetic architecture is shared among distylous species is critical. 

主要研究：Here, we have characterized the genetic architecture and evolution of the distyly supergene in Linum by generating a chromosome-level genome assembly of Linum tenue, followed by the identification of the S-locus using population genomic data. 

结果1-突变体库筛选：We show that hemizygosity and thrum-specific expression of S-linked genes, including a pistil-expressed candidate gene for style length, are major features of the Linum S-locus. Structural variation is likely instrumental for recombination suppression, and although the non-recombining dominant haplotype has accumulated transposable elements, S-linked genes are not under relaxed purifying selection. 

结论：Our findings reveal remarkable convergence in the genetic architecture and evolution of independently derived distyly supergenes, provide a counterexample to classic inversion-based supergenes, and shed new light on the origin and maintenance of an iconic floral polymorphism.

Figure 1. Distyly in Linum tenue.

超基因在很多系统中作用于多性状平衡多态性的控制；然而，我们对其起源和演化的理解仍不清晰。二型花柱植物长花柱（pin型）和短花柱（thrum型）的柱头和花药相互的替换构成了一个平衡多态的典型实例，该表型由一个超基因二型花柱S基因座控制。最近的研究表明，报春花属和时钟花属植株的二型花柱超基因都是属于半合子，但仍不清楚半合子是否是二型花柱S基因座普遍存在的。由于半合子对超基因的演化和丢失具有重大影响，因此鉴明这种遗传结构是否是二型花柱植物普遍存在情况至关重要。本文中，作者获得了亚麻属植物Linum tenue的染色体级别基因组，并通过群体基因组数据鉴定到了其控制二型花柱的S基因座，鉴定了该物种二型花柱超基因的遗传结构和演化。结果表明，Linum S基因位点较为显著的特征表现为半合子以及S连锁基因的短花柱特异性表达，包括一个在雌蕊中表达的花柱长度候选基因。结构变异可能有助于抑制重组，尽管非重组显性单倍型积累了转座元件，但S连锁基因不处于宽松的纯化选择下。本文的研究结果揭示了独立起源的二型花柱超基因的遗传结构和演化上的趋同性，为经典的超基因倒位来源提供了反例，并为标志性花多态性的起源和维持提供了新的视野。

 Tanja Slotte