Tao Jiayi, Zhang Liangran, Chong Kang, Wang Tai
Research Center for Molecular and Developmental Biology, Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, 20 Nanxincun, Xiangshan, Haidianqu, Beijing, China.
Plant J. 2007 Sep;51(5):919-30. doi: 10.1111/j.1365-313X.2007.03190.x. Epub 2007 Jul 7.
In contrast to animals, in which products of meiosis differentiate directly into sperm, flowering plants employ a specific mechanism to give rise to functional sperm cells, the specifics of which remain largely unknown. A previous study revealed that, compared to yeast and vertebrates, which have two proteins (Rad21 and its meiosis-specific variant Rec8) that play a vital role in sister chromatid cohesion and segregation for mitosis and meiosis, respectively, the rice genome encodes four Rad21/Rec8 proteins (OsRad21s). In this paper, phylogenetic and immunostaining analyses reveal that OsRad21-3 is an orthologue of yeast Rad21. OsRAD21-3 transcript and protein accumulated preferentially in flowers, with low levels in vegetative tissues. In flowers, they persisted from the stamen and carpel primordia stages until the mature pollen stage. OsRAD21-3-deficient RNAi lines showed arrested pollen mitosis, aberrant pollen chromosome segregation and aborted pollen grains, which led to disrupted pollen viability. However, male meiosis in these RNAi lines did not appear to be severely disrupted, which suggests that the main involvement of OsRAD21-3 is in post-meiotic pollen development by affecting pollen mitosis. Furthermore, of the four OsRAD21 genes in the rice genome, only OsRAD21-3 was expressed in pollen grains. Given that the mechanism involving generation of sperm cells differs between flowering plants and metozoans, this study shows, in part, why flowering plants of rice and Arabidopsis have four Rad21/Rec8 proteins, as compared with two in yeast and metozoans, and gives some clues to the functional differentiation of Rad21/Rec8 proteins during evolution.
与动物不同,动物减数分裂的产物直接分化为精子,开花植物则采用一种特定机制来产生功能性精子细胞,但其具体细节在很大程度上仍不清楚。先前的一项研究表明,与酵母和脊椎动物相比,酵母和脊椎动物分别有两种蛋白质(Rad21及其减数分裂特异性变体Rec8)在有丝分裂和减数分裂的姐妹染色单体黏连和分离中起关键作用,而水稻基因组编码四种Rad21/Rec8蛋白质(OsRad21s)。在本文中,系统发育和免疫染色分析表明,OsRad21-3是酵母Rad21的直系同源物。OsRAD21-3转录本和蛋白质优先在花中积累,在营养组织中含量较低。在花中,它们从雄蕊和心皮原基阶段持续到成熟花粉阶段。OsRAD21-3缺陷的RNAi株系表现出花粉有丝分裂停滞、花粉染色体分离异常和花粉粒败育,这导致花粉活力受到破坏。然而,这些RNAi株系中的雄性减数分裂似乎并未受到严重破坏,这表明OsRad21-3主要通过影响花粉有丝分裂参与减数分裂后的花粉发育。此外,在水稻基因组的四个OsRAD21基因中,只有OsRAD21-3在花粉粒中表达。鉴于开花植物和后生动物产生精子细胞的机制不同,这项研究部分说明了为什么水稻和拟南芥的开花植物有四种Rad21/Rec8蛋白质,而酵母和后生动物只有两种,并为Rad21/Rec8蛋白质在进化过程中的功能分化提供了一些线索。