Tsuchikane Yuki, Tsuchiya Miki, Hindák František, Nozaki Hisayoshi, Sekimoto Hiroyuki
Department of Chemical and Biological Sciences, Faculty of Science, Japan Women's University, 2-8-1 Mejirodai, Bunkyo-ku, Tokyo 112 8681, Japan.
Sex Plant Reprod. 2012 Mar;25(1):1-9. doi: 10.1007/s00497-011-0174-z. Epub 2011 Aug 20.
Zygospore formation in different strains of the Closterium peracerosum-strigosum-littorale complex was examined in this unicellular isogamous charophycean alga to shed light on gametic mating strains in this taxon, which is believed to share a close phylogenetic relationship with land plants. Zygospores typically form as a result of conjugation between mating-type plus (mt(+)) and mating-type minus (mt(-)) cells during sexual reproduction in the heterothallic strain, similar to Chlamydomonas. However, within clonal cells, zygospores are formed within homothallic strains, and the majority of these zygospores originate as a result of conjugation of two recently divided sister gametangial cells derived from one vegetative cell. In this study, we analyzed conjugation of homothallic cells in the presence of phylogenetically closely related heterothallic cells to characterize the reproductive function of homothallic sister gametangial cells. The relative ratio of non-sister zygospores to sister zygospores increased in the presence of heterothallic mt(+) cells, compared with that in the homothallic strain alone and in a coculture with mt(-) cells. Heterothallic cells were surface labeled with calcofluor white, permitting fusions with homothallic cells to be identified and confirming the formation of hybrid zygospores between the homothallic cells and heterothallic mt(+) cells. These results show that at least some of the homothallic gametangial cells possess heterothallic mt(-)-like characters. This finding supports speculation that division of one vegetative cell into two sister gametangial cells is a segregative process capable of producing complementary mating types.
在这种单细胞同配的轮藻纲藻类中，研究了不同菌株的纤细新月藻-条纹新月藻-滨海新月藻复合体中的接合孢子形成，以阐明该分类单元中的配子交配菌株，据信该分类单元与陆地植物有着密切的系统发育关系。与衣藻类似，在异宗配合菌株的有性生殖过程中，接合孢子通常是由正交配型（mt(+)）和负交配型（mt(-)）细胞之间的接合形成的。然而，在克隆细胞内，同宗配合菌株中会形成接合孢子，并且这些接合孢子中的大多数是由源自一个营养细胞的两个最近分裂的姐妹配子囊细胞接合产生的。在本研究中，我们分析了在系统发育上密切相关的异宗配合细胞存在的情况下同宗配合细胞的接合，以表征同宗配合姐妹配子囊细胞的生殖功能。与单独的同宗配合菌株以及与mt(-)细胞共培养相比，在异宗配合的mt(+)细胞存在的情况下，非姐妹接合孢子与姐妹接合孢子的相对比例增加。用荧光增白剂对异宗配合细胞进行表面标记，从而能够识别与同宗配合细胞的融合，并确认同宗配合细胞与异宗配合的mt(+)细胞之间形成了杂种接合孢子。这些结果表明，至少一些同宗配合的配子囊细胞具有类似异宗配合mt(-)的特征。这一发现支持了这样的推测，即一个营养细胞分裂成两个姐妹配子囊细胞是一个能够产生互补交配类型的分离过程。
