Jamilena M, Mariotti B, Manzano S
Departamento de Biología Aplicada, Area de Genética, Escuela Politécnica Superior, Universidad de Almería, Almería, Spain.
Cytogenet Genome Res. 2008;120(3-4):255-64. doi: 10.1159/000121075. Epub 2008 May 23.
Recent molecular and genomic studies carried out in a number of model dioecious plant species, including Asparagus officinalis, Carica papaya, Silene latifolia, Rumex acetosa and Marchantia polymorpha, have shed light on the molecular structure of both homomorphic and heteromorphic sex chromosomes, and also on the gene functions they have maintained since their evolution from a pair of autosomes. The molecular structure of sex chromosomes in species from different plant families represents the evolutionary pathway followed by sex chromosomes during their evolution. The degree of Y chromosome degeneration that accompanies the suppression of recombination between the Xs and Ys differs among species. The primitive Ys of A. officinalis and C. papaya have only diverged from their homomorphic Xs in a short male-specific and non-recombining region (MSY), while the heteromorphic Ys of S. latifolia, R. acetosa and M. polymorpha have diverged from their respective Xs. As in the Y chromosomes of mammals and Drosophila, the accumulation of repetitive DNA, including both transposable elements and satellite DNA, has played an important role in the divergence and size enlargement of plant Ys, and consequently in reducing gene density. Nevertheless, the degeneration process in plants does not appear to have reached the Y-linked genes. Although a low gene density has been found in the sequenced Y chromosome of M. polymorpha, most of its genes are essential and are expressed in the vegetative and reproductive organs in both male and females. Similarly, most of the Y-linked genes that have been isolated and characterized up to now in S. latifolia are housekeeping genes that have X-linked homologues, and are therefore expressed in both males and females. Only one of them seems to be degenerate with respect to its homologous region in the X. Sequence analysis of larger regions in the homomorphic X and Y chromosomes of papaya and asparagus, and also in the heteromorphic sex chromosomes of S. latifolia and R. acetosa, will reveal the degenerative changes that the Y-linked gene functions have experienced during sex chromosome evolution.
最近在包括芦笋、番木瓜、宽叶蝇子草、酸模和多形苔等多种雌雄异株模式植物物种中开展的分子和基因组研究，揭示了同形和异形性染色体的分子结构，以及自其从一对常染色体进化而来后所保留的基因功能。不同植物科物种的性染色体分子结构代表了性染色体在进化过程中所遵循的进化途径。伴随X和Y染色体间重组抑制而发生的Y染色体退化程度在不同物种间存在差异。芦笋和番木瓜的原始Y染色体仅在短的雄性特异性非重组区域（MSY）与其同形X染色体发生了分化，而宽叶蝇子草、酸模和多形苔的异形Y染色体则与其各自的X染色体发生了分化。与哺乳动物和果蝇的Y染色体一样，包括转座元件和卫星DNA在内的重复DNA积累，在植物Y染色体的分化和大小增大中发挥了重要作用，从而降低了基因密度。然而，植物中的退化过程似乎尚未波及Y连锁基因。尽管在多形苔已测序的Y染色体中发现基因密度较低，但其大多数基因是必需的，且在雄性和雌性的营养器官和生殖器官中均有表达。同样，到目前为止在宽叶蝇子草中分离和鉴定的大多数Y连锁基因都是具有X连锁同源物的管家基因，因此在雄性和雌性中均有表达。其中只有一个基因相对于其在X染色体中的同源区域似乎发生了退化。对番木瓜和芦笋同形X和Y染色体以及宽叶蝇子草和酸模异形性染色体更大区域的序列分析，将揭示Y连锁基因功能在性染色体进化过程中所经历的退化变化。
