Mariotti Beatrice, Manzano Susana, Kejnovský Eduard, Vyskot Boris, Jamilena Manuel
Departamento de Biología Aplicada, Escuela Politécnica Superior, Universidad de Almería, 04120, Almería, Spain.
Mol Genet Genomics. 2009 Mar;281(3):249-59. doi: 10.1007/s00438-008-0405-7. Epub 2008 Dec 16.
The study of the molecular structure of young heteromorphic sex chromosomes of plants has shed light on the evolutionary forces that control the differentiation of the X and Y during the earlier stages of their evolution. We have used the model plant Rumex acetosa, a dioecious species with multiple sex chromosomes, 2n = 12 + XX female and 2n = 12 + XY(1)Y(2) male, to analyse the significance of repetitive DNA accumulation during the differentiation of the Y. A bulk segregant analysis (BSA) approach allowed us to identify and isolate random amplified polymorphic DNA (RAPD) markers linked to the sex chromosomes. From a total of 86 RAPD markers in the parents, 6 markers were found to be linked to the Ys and 1 to the X. Two of the Y-linked markers represent two AT-rich satellite DNAs (satDNAs), named RAYSII and RAYSIII, that share about 80% homology, as well as with RAYSI, another satDNA of R. acetosa. Fluorescent in situ hybridisation demonstrated that RAYSII is specific for Y(1), whilst RAYSIII is located in different clusters along Y(1) and Y(2). The two satDNAs were only detected in the genome of the dioecious species with XX/XY(1)Y(2) multiple sex chromosome systems in the subgenus Acetosa, but were absent from other dioecious species with an XX/XY system of the subgenera Acetosa or Acetosella, as well as in gynodioecious or hermaphrodite species of the subgenera Acetosa, Rumex and Platypodium. Phylogenetic analysis with different cloned monomers of RAYSII and RAYSIII from both R. acetosa and R. papillaris indicate that these two satDNAs are completely separated from each other, and from RAYSI, in both species. The three Y-specific satDNAs, however, evolved from an ancestral satDNA with repeating units of 120 bp, through intermediate satDNAs of 360 bp. The data therefore support the idea that Y-chromosome differentiation and heterochromatinisation in the Rumex species having a multiple sex chromosome system have occurred by different amplification events from a common ancestral satDNA. Since dioecious species with multiple XX/XY(1)Y(2) sex chromosome systems of the section Acetosa appear to have evolved from dioecious species with an XX/XY system, the amplification of tandemly repetitive elements in the Ys of the section Acetosa is a recent evolutionary process that has contributed to an increase in the size and differentiation of the already non-recombining Y chromosomes.
对植物年轻的异形性染色体分子结构的研究，揭示了在其进化早期控制X和Y染色体分化的进化力量。我们使用了模式植物酸模（Rumex acetosa），这是一种具有多条性染色体的雌雄异株物种，雌性为2n = 12 + XX，雄性为2n = 12 + XY(1)Y(2)，来分析Y染色体分化过程中重复DNA积累的意义。一种混合分离分析（BSA）方法使我们能够鉴定并分离出与性染色体连锁的随机扩增多态性DNA（RAPD）标记。在亲本的总共86个RAPD标记中，发现6个标记与Y染色体连锁，1个与X染色体连锁。两个与Y染色体连锁的标记代表两种富含AT的卫星DNA（satDNA），分别命名为RAYSII和RAYSIII，它们具有约80%的同源性，并且与酸模的另一种satDNA RAYSI也有同源性。荧光原位杂交表明，RAYSII特异性定位于Y(1)，而RAYSIII沿着Y(1)和Y(2)分布在不同的簇中。这两种satDNA仅在酸模亚属中具有XX/XY(1)Y(2)多条性染色体系统的雌雄异株物种的基因组中检测到，而在酸模亚属或酸模叶亚属具有XX/XY系统的其他雌雄异株物种中，以及在酸模亚属、酸模属和扁柄草属的雌全同株或雌雄同体物种中均未发现。对来自酸模和乳头酸模的RAYSII和RAYSIII不同克隆单体进行的系统发育分析表明，在这两个物种中，这两种satDNA彼此完全分离，并且与RAYSI也完全分离。然而，这三种Y特异性satDNA是从一个具有120 bp重复单元的祖先satDNA，通过360 bp的中间satDNA进化而来的。因此，这些数据支持了这样一种观点，即在具有多条性染色体系统的酸模属物种中，Y染色体的分化和异染色质化是通过来自一个共同祖先satDNA的不同扩增事件发生的。由于酸模组中具有XX/XY(1)Y(2)多条性染色体系统的雌雄异株物种似乎是从具有XX/XY系统的雌雄异株物种进化而来的，酸模组Y染色体上串联重复元件的扩增是一个最近的进化过程，它促进了已经不发生重组的Y染色体的大小增加和分化。
