Temasek LifeScience Laboratory, 1 Research Link , National University of Singapore , 117604 Singapore.
AoB Plants. 2011;2011:plr015. doi: 10.1093/aobpla/plr015. Epub 2011 Jun 22.
Flowering plant seeds originate from a unique double-fertilization event, which involves two sperm cells and two female gametes, the egg cell and the central cell. For many years our knowledge of mechanisms involved in angiosperm fertilization remained minimal. It was obvious that several signals were required to explain how the male gametes are delivered inside the maternal reproductive tissues to the two female gametes but their molecular nature remained unknown. The difficulties in imaging the double-fertilization process prevented the identification of the mode of sperm cell delivery. It was believed that the two sperm cells were not functionally equivalent.
We review recent studies that have significantly improved our understanding of the early steps of double fertilization. The attractants of the pollen tube have been identified as small proteins produced by the synergid cells that surround the egg cell. Genetic studies have identified the signalling pathways required for the release of male gametes from the pollen tube. High-resolution imaging of the trajectory of the two male gametes showed that their transport does not involve the synergid cells directly and that isomorphic male gametes are functionally equivalent. We also outline major outstanding issues in the field concerned with the barrier against polyspermy, gamete recognition and mechanisms that prevent interspecies crosses.
开花植物的种子来源于一个独特的双受精事件，涉及两个精子细胞和两个雌性配子，即卵子和中央细胞。多年来，我们对被子植物受精过程中涉及的机制的了解仍然很少。显然，需要有几个信号来解释雄性配子如何被输送到母性生殖组织内的两个雌性配子中，但它们的分子性质仍然未知。由于难以对双受精过程进行成像，因此无法确定精子细胞输送的模式。人们认为两个精子细胞在功能上并不等同。
我们回顾了最近的研究，这些研究显著提高了我们对双受精早期步骤的理解。花粉管的吸引剂已被鉴定为环绕卵子的助细胞产生的小蛋白质。遗传研究已经确定了从花粉管释放雄性配子所需的信号通路。对两条雄性配子的轨迹进行高分辨率成像表明，它们的运输不涉及助细胞直接参与，并且同形雄性配子在功能上是等同的。我们还概述了该领域中与多精入卵障碍、配子识别以及防止种间杂交的机制有关的主要未决问题。
