Graduate School of Environmental and Life Science, Okayama University, Okayama, Japan.
Department of Frontier Research and Development, Kazusa DNA Research Institute, Chiba, Japan.
Mol Biol Evol. 2023 Jul 3;40(7). doi: 10.1093/molbev/msad151.
Plants have evolved sex chromosomes independently in many lineages, and loss of separate sexes can also occur. In this study, we assembled a monoecious recently hexaploidized persimmon (Diospyros kaki), in which the Y chromosome has lost the maleness-determining function. Comparative genomic analysis of D. kaki and its dioecious relatives uncovered the evolutionary process by which the nonfunctional Y chromosome (or Ymonoecy) was derived, which involved silencing of the sex-determining gene, OGI, approximately 2 million years ago. Analyses of the entire X and Ymonoecy chromosomes suggested that D. kaki's nonfunctional male-specific region of the Y chromosome (MSY), which we call a post-MSY, has conserved some characteristics of the original functional MSY. Specifically, comparing the functional MSY in Diospyros lotus and the nonfunctional "post-MSY" in D. kaki indicated that both have been rapidly rearranged, mainly via ongoing transposable element bursts, resembling structural changes often detected in Y-linked regions, some of which can enlarge the nonrecombining regions. The recent evolution of the post-MSY (and possibly also MSYs in dioecious Diospyros species) therefore probably reflects these regions' ancestral location in a pericentromeric region, rather than the presence of male-determining genes and/or genes controlling sexually dimorphic traits.
植物在许多谱系中独立进化出性染色体，也可能失去独立的性别。在这项研究中，我们组装了一个雌雄同体的新近六倍体柿（Diospyros kaki），其中 Y 染色体失去了雄性决定功能。对 D. kaki 和其雌雄异株的近亲进行比较基因组分析，揭示了非功能 Y 染色体（或 Ymonoecy）的进化过程，大约在 200 万年前，该过程涉及到性别决定基因 OGI 的沉默。对整个 X 和 Ymonoecy 染色体的分析表明，D. kaki 的 Y 染色体非功能雄性特异性区域（MSY），我们称之为后 MSY，保留了一些原始功能 MSY 的特征。具体来说，比较 Diospyros lotus 中的功能 MSY 和 D. kaki 中的非功能“后 MSY”表明，两者都经历了快速的重排，主要通过持续的转座元件爆发，类似于通常在 Y 连锁区域检测到的结构变化，其中一些可以扩大非重组区域。因此，后 MSY（可能还有雌雄异株的 Diospyros 物种中的 MSY）的近期进化可能反映了这些区域在着丝粒区域的祖先位置，而不是雄性决定基因和/或控制性二态特征的基因的存在。
