Graduate School of Environmental and Life Science, Okayama University, Okayama, Japan.
Japan Science and Technology Agency (JST), PRESTO, Kawaguchi-shi, Saitama, Japan.
PLoS Genet. 2020 Feb 18;16(2):e1008566. doi: 10.1371/journal.pgen.1008566. eCollection 2020 Feb.
Most angiosperms bear hermaphroditic flowers, but a few species have evolved outcrossing strategies, such as dioecy, the presence of separate male and female individuals. We previously investigated the mechanisms underlying dioecy in diploid persimmon (D. lotus) and found that male flowers are specified by repression of the autosomal gene MeGI by its paralog, the Y-encoded pseudo-gene OGI. This mechanism is thought to be lineage-specific, but its evolutionary path remains unknown. Here, we developed a full draft of the diploid persimmon genome (D. lotus), which revealed a lineage-specific whole-genome duplication event and provided information on the architecture of the Y chromosome. We also identified three paralogs, MeGI, OGI and newly identified Sister of MeGI (SiMeGI). Evolutionary analysis suggested that MeGI underwent adaptive evolution after the whole-genome duplication event. Transformation of tobacco plants with MeGI and SiMeGI revealed that MeGI specifically acquired a new function as a repressor of male organ development, while SiMeGI presumably maintained the original function. Later, a segmental duplication event spawned MeGI's regulator OGI on the Y-chromosome, completing the path leading to dioecy, and probably initiating the formation of the Y-chromosome. These findings exemplify how duplication events can provide flexible genetic material available to help respond to varying environments and provide interesting parallels for our understanding of the mechanisms underlying the transition into dieocy in plants.
大多数被子植物都具有两性花，但有少数物种进化出了异交策略，例如雌雄异株，即存在单独的雄性和雌性个体。我们之前研究了二倍体柿子（Diospyros lotus）雌雄异株的机制，发现雄性花是由常染色体基因 MeGI 与其 Y 编码的假基因 OGI 的抑制所决定的。这种机制被认为是谱系特异性的，但它的进化途径仍然未知。在这里，我们开发了二倍体柿子的全基因组草图（D. lotus），揭示了一个谱系特异性的全基因组复制事件，并提供了 Y 染色体结构的信息。我们还鉴定了三个基因的三个同源基因，MeGI、OGI 和新鉴定的 MeGI 姐妹基因（SiMeGI）。进化分析表明，MeGI 在全基因组复制事件后经历了适应性进化。用 MeGI 和 SiMeGI 转化烟草植物表明，MeGI 特异性地获得了抑制雄性器官发育的新功能，而 SiMeGI 可能维持了原来的功能。后来，一个片段重复事件在 Y 染色体上产生了 MeGI 的调控基因 OGI，完成了导致雌雄异株的途径，并可能启动了 Y 染色体的形成。这些发现例证了重复事件如何提供灵活的遗传物质，以帮助应对不断变化的环境，并为我们理解植物雌雄异株的机制提供了有趣的类比。
