双受精（Double fertilization）是一种在生物学上具有独特意义的生殖系统，被认为是开花植物演化中的一个关键创新。与动物受精不同的是，双受精涉及一对精细胞通过不同子细胞的选择性分裂的生成。
现在，一种新的F-box蛋白，名为FBL17，被发现在拟南芥中能促进双精细胞的生成。在雄性生殖细胞中，FBL17以KRP7为目标，后者是依赖于细胞周期蛋白的激酶的一个抑制因子。开花植物所用的这一细胞周期调控机制在酵母和动物细胞之间是在演化上保留下来的，这项新的研究工作说明了调控机制是怎样演化来适应特殊环境的。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature 455, 1134-1137 (23 October 2008) | doi:10.1038/nature07289
Control of plant germline proliferation by SCFFBL17 degradation of cell cycle inhibitors
Hyo Jung Kim1, Sung Aeong Oh3,4, Lynette Brownfield3, Sung Hyun Hong1, Hojin Ryu1, Ildoo Hwang1, David Twell3 & Hong Gil Nam1,2
1 Division of Molecular Life Sciences,
2 School of Interdisciplinary Bioscience and Bioengineering, Pohang University of Science and Technology, Pohang 790-784, South Korea
3 Department of Biology, University of Leicester, University Road, Leicester LE1 7RH, UK
4 Present address: School of Life Sciences, Kyungpook National University, Daegu 702-701, South Korea.
Flowering plants possess a unique reproductive strategy, involving double fertilization by twin sperm cells1. Unlike animal germ lines, the male germ cell lineage in plants only forms after meiosis and involves asymmetric division of haploid microspores, to produce a large, non-germline vegetative cell and a germ cell that undergoes one further division to produce the twin sperm cells2. Although this switch in cell cycle control is critical for sperm cell production and delivery, the underlying molecular mechanisms are unknown. Here we identify a novel F-box protein ofArabidopsis thaliana, designated FBL17 (F-box-like 17), that enables this switch by targeting the degradation of cyclin-dependent kinase A;1 inhibitors specifically in male germ cells. We show that FBL17 is transiently expressed in the male germ line after asymmetric division and forms an SKP1–Cullin1–F-box protein (SCF) E3 ubiquitin ligase complex (SCFFBL17) that targets the cyclin-dependent kinase inhibitors KRP6 and KRP7 for proteasome-dependent degradation. Accordingly, the loss of FBL17 function leads to the stabilization of KRP6 and inhibition of germ cell cycle progression. Our results identify SCFFBL17 as an essential male germ cell proliferation complex that promotes twin sperm cell production and double fertilization in flowering plants.
