Time Bomb for Pollen Tubes: Peptide RALF-Mediated Signaling
Time Bomb for Pollen Tubes: Peptide RALF-Mediated Signaling
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花粉管的定时炸弹：肽 RALF 介导的信号传导
DOI：
10.1016/j.molp.2018.02.010
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发表时间：
2018
期刊：
影响因子：
27.5
通讯作者：
Wang Hao
中科院分区：
文献类型：
--
作者：
Peng Xiaomin;Li Shanshan;Wang Hao
为了实现有性繁殖，开花植物进化出了独特的双受精系统，这与动物不同。花粉是被子植物的雄性配子体，含有两个不动的精子细胞，是雌雄相通的媒介。落在花的柱头上后，它立即发芽并形成一个高度极化且快速生长的花粉管，将精子细胞传递给嵌入胚珠深处的雌性配子（Dresselhaus et al., 2016）。在花粉管生长过程中，花粉管与胚珠之间的通讯和信号在时间和空间上受到严格调控，从而保证了受精的成功。长期以来，花粉管是如何精确地定位它们的目的地，并按时释放两个精子细胞的，这一直困扰着生物学家。过去20年的研究发现，雌性配子释放的多态肽与花粉管表面受体之间的相互作用在花粉管的吸引和靶向中起主导作用（Okuda et al., 2009; Takeuchi and Higashiyama, 2016; Wang et al., 2016）。虽然已经确定了调控花粉管完整性的多种因素，但控制花粉管破裂的工作原理和潜在的具体机制仍然难以捉摸（Muschietti和Wengier， 2017）。近年来，有关花粉管破裂和精子排出信号分子的报道陆续发表（Ge et al., 2017; mecia et al., 2017）。这些研究提供了对植物花粉管完整性调控以确保成功双受精过程的更全面的理解，并提高了我们对植物雄性和雌性配子之间信号相互作用复杂性的认识。据报道，小分泌肽在整个花粉管通路中起着显性信号分子的作用，包括自交不亲和反应、胚珠花粉管引导和雌性配子体的花粉管接收。通常，它们通过常规分泌途径合成并分泌到细胞外空间。此后，它们扩散到邻近细胞特异性结合并激活其同源受体，从而引发下游细胞内信号传导反应。与已被充分研究的肽相比，它们在雄性-雌性交流和受精过程中的相互作用受体的特征和理解较少。受体样激酶（Receptor-like kinase, RLKs）是一个大的跨膜蛋白家族，在控制植物发育、对环境胁迫的反应、激素感知和自交不亲和性中起着重要作用（Gish and Clark, 2011; Haruta et al., 2014）。最近，突破性研究发现了多组花花管特异性RLKs，它们可以与女性器官释放的富含半胱氨酸的肽AtLURE1相互作用，并在花花管生长中充当吸引剂的传感器（Takeuchi和Higashiyama, 2016; Wang et al., 2016）。然而，信号肽和RLKs的武器库
To achieve sexual reproduction, flowering plants have evolved a unique double fertilization system that is distinct from animals. Pollen, the male gametophyte of angiosperms, contains two immobile sperm cells and functions as a vehicle for male–female interconnection. Upon landing on the stigma of a flower, it immediately germinates and forms a highly polarized and rapidly growing pollen tube, which delivers the sperm cells to the female gametes embedded deep in the ovules (Dresselhaus et al., 2016). The communication and signaling between the pollen tube and the ovule are temporally and spatially tightly regulated at multiple steps during the growth of the pollen tube to ensure the success of the fertilization. How pollen tubes precisely target their destination and release two sperm cells on time has long puzzled biologists. Elegant studies over the past 20 years have identified that the interactions between polymorphic peptides released from the female gametes and receptors at the pollen tube surface play a leading role in attracting and targeting of pollen tubes (Okuda et al., 2009; Takeuchi and Higashiyama, 2016; Wang et al., 2016). Although multiple factors for regulating pollen tube integrality have been identified, the working rationale and underlying specific mechanisms of controlling pollen tube rupture still remain elusive (Muschietti and Wengier, 2017). Recently, reports on the signaling molecules leading to pollen tube burst and sperm discharge have been published (Ge et al., 2017; Mecchia et al., 2017). These studies provide a more comprehensive understanding of the process that regulates pollen tube integrity to ensure successful double fertilization in plants, and have advanced our knowledge regarding the complexity of the signaling interactions between plant male and female gametes.Small secreted peptides have been reported to function as dominant signaling molecules along the whole pollen tube pathway, including self-incompatibility responses, ovular pollen tube guidance, and pollen tube reception by the female gametophyte. Usually, they are synthesized and exocytosed into the extracellular space through the conventional secretion pathway. Thereafter, they diffuse to neighborhood cells to specifically bind and activate their cognate receptors to trigger downstream intracellular signaling reactions. In contrast to the well-studied peptides, their interacting receptors during the male–female communications and fertilization are less characterized and understood. Receptor-like kinases (RLKs) are a large transmembrane protein family and have vital roles in controlling plant development, responses to environmental stresses, hormone perception, and self-incompatibility (Gish and Clark, 2011; Haruta et al., 2014). Recently, breakthrough studies have identified multiple sets of pollen-tube-specific RLKs that can interact with the femaleorgan-released cysteine-rich peptide AtLURE1 and act as a sensor for the attractant in navigating pollen tube growth (Takeuchi and Higashiyama, 2016; Wang et al., 2016). However, the arsenal of signaling peptides and RLKs during the