Plant Journal:中科院刘春明研究组发现植物合子激活重要调控机制
2016年4月6日,国际植物学权威期刊《The plant Journal》在线发表中国科学院植物分子生理学重点实验室刘春明组博士发表的一篇研究论文，论文揭示了植物合子激活重要调控机制。刘春明组博士研究生郭磊与蒋丽为该论文的共同第一作者。
合子激活是一个新生命的起始。在植物的双受精过程中，来自花粉管的两个精细胞分别与卵细胞和中央核融合，经过分裂与分化形成胚胎和胚乳。尽管之前的研究已经找到数个影响合子分裂的基因，但其调控机制尚不清楚。刘春明课题组通过遗传学筛选获得多个合子致死突变体，对其中zygote-arrest 1(zyg1)的研究结果显示蛋白降解复合体APC/C复合体APC11亚基调控合子激活。APC11主要表达于胚胎、胚乳、根尖、茎尖等细胞分裂活跃的部位，其突变造成cyclinB1在胚胎和胚乳中累积。进一步的研究发现APC11具有泛素修饰酶活性，并可以直接泛素修饰和降解CYCB1;1。在胚胎中表达不能被降解的CYCB1;1的转基因植物呈现与zyg1突变体相似的合子败育表型。以上结果表明APC/C复合体通过调控细胞周期蛋白CYCB1;1的降解来启动植物的合子激活。
图. (a)和(b), 正常(a)和zyg1突变体(b)，显示zyg1的合子败育，(c) CYCB1-GUS在ZYG1/zyg1突变体角果很多胚珠中累积，(d) 野生型和ZYG1/zyg1突变体植物角果中出现CYCB1-GUS累积胚珠的比例明显不同，(e)和(f), CYCB1-GUS在正常(e)和败育胚珠(f)中的累积。
原文链接：
The anaphase promoting complex initiates zygote division in ArABIdopsis through degradation of cyclin B1
原文摘要：
As the starting point of a new life cycle, activation of the first division of the zygote is a critical event in both plants and animals. Due to poor accessibility of the zygote in plants, how this process is achieved remains poorly understood. Here we report genetic and cell biological analyses of the zygote-arrest 1 (zyg1) mutant in Arabidopsis, which showed zygote-lethal and over-accumulation of cyclin B1 D-box-GUS in ovules. Map-based cloning showed that ZYG1 encodes the anaphase promoting complex/cyclosome (APC/C) subunit 11 (APC11). Live-cell imaging studies showed that APC11 is expressed in both egg and sperm cells, in zygotes and during early embryogenesis. Using a GFP-APC11 fusion construct that fully complement zyg1, we showed thatGFP-APC11 expression persisted throughout the mitotic cell cycle, and localized to cell plates during cytokinesis. Expression of non-degradable cyclin B1 in zygote, or mutations of either APC1or APC4, also led to a zyg1-like phenotype. Biochemical studies showed that APC11 has self-ubiquitination activity, and is able to ubiquitinate cyclin B1 and promote cyclin B1 degradation. These results together suggest that APC/C-mediated cyclin B1 degradation in Arabidopsis is critical for initiating the first division of the zygote.
作者：刘春明
