背景回顾：Sex determination is a central process for sexual reproduction and is often regulated by a sex determinant encoded on a sex chromosome. Rules that govern the evolution of sex chromosomes via specialization and degeneration following the evolution of a sex determinant have been well studied in diploid organisms. 

提出问题：However, distinct predictions apply to sex chromosomes in organisms where sex is determined in the haploid phase of the life cycle: both sex chromosomes, female U and male V, are expected to maintain their gene functions, even though both are non-recombining. This is in contrast to the X-Y (or Z-W) asymmetry and Y (W) chromosome degeneration in XY (ZW) systems of diploids. 

主要发现：Here, we provide evidence that sex chromosomes diverged early during the evolution of haploid liverworts and identify the sex determinant on the Marchantia polymorpha U chromosome. 

结果1-性别决定基因：This gene, Feminizer, encodes a member of the plant-specific BASIC PENTACYSTEINE transcription factor family. 

结果2-作用机制：It triggers female differentiation via regulation of the autosomal sex-determining locus of FEMALE GAMETOPHYTE MYB and SUPPRESSOR OF FEMINIZATION. 

结果3-演化历史：Phylogenetic analyses of Feminizer and other sex chromosome genes indicate dimorphic sex chromosomes had already been established 430 mya in the ancestral liverwort.

结果4-祖先功能：Feminizer also plays a role in reproductive induction that is shared with its gametolog on the V chromosome, suggesting an ancestral function, distinct from sex determination, was retained by the gametologs. This implies ancestral functions can be preserved after the acquisition of a sex determination mechanism during the evolution of a dominant haploid sex chromosome system.

 摘 要 

性别决定是有性生殖的核心进程，通常是由性染色体上编码的性别决定因素所调控。在二倍体生物中，性别决定因素演化后，通由基因功能特化和退化来影响性染色体演化的生物规则已经研究得比较深入了。但是，对于性别是在生命周期中的单倍体时期所决定的生物而言，采取了不同于二倍体的策略，其中尽管雌性U和雄性V这两条性染色体都不会发生重组，但是二者都被认为能够保持其基因功能。这与二倍体的X-Y（或者Z-W）不对称和XY（ZW）系统中Y（W）染色体退化不同。本文中，作者发现单倍体地钱演化早期就出现了性染色体的分化，并且鉴定到了地钱（Marchantia polymorpha）U染色体上的性别决定因子。该基因Feminizer是编码植物特异性BASIC PENTACYSTEINE转录因子家族的一个成员。Feminizer通过对常染色体性别决定位点上FEMALE GAMETOPHYTE MYB和SUPPRESSOR OF FEMINIZATION基因的调控来诱导雌性分化。通过对Feminizer和其它性染色体基因的系统发育分析，作者发现大约在4亿3千万年前的祖先地钱中，已经建立起了二态性染色体。Feminizer同时还在生殖诱导中起作用，与其在V染色体上的配子体同源基因的功能一致，表明配子体同源基因除了性别决定之前，还保留了一个祖先的功能。这表明，在显性单倍体性染色体系统的演化过程中，在获得性别决定机制后，祖先的功能也可以得以保留。