Vol.:(0123456789) 1 3 Plant Reproduction (2018) 31:31–41 https://doi.org/10.1007/s00497-018-0324-7 REVIEW Multilayered signaling pathways for pollen tube growth and guidance Hong‑Ju Li 1,2  · Jiang‑Guo Meng 1,2  · Wei‑Cai Yang 1,2 Received: 7 November 2017 / Accepted: 24 January 2018 / Published online: 13 February 2018 © Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract Sexual reproductive success is essential for the survival of all higher organisms. As the most prosperous and diverse group of land plants on earth, fowering plants evolved highly sophisticated fertilization mechanisms. To adapt to the terrestrial environment, a tubular structure pollen tube has been evolved to deliver the immobile sperm cells to the egg and central cell enclosed within the ovule. The pollen tube is generated from the vegetative cell of the pollen (male gametophyte), where two sperm cells are hosted. Pollen tube elongation in the maternal tissue and navigation to the ovule require intimate cell–cell interactions between the tube and female tissues. Questions on how the single-celled pollen tube accomplishes such task and how the female tissues accommodate the tube have attracted many plant biologists. Here, we review recent progresses and concepts in understanding the molecular mechanisms governing pollen tube growth and its interactions with the female tissues. We will also discuss the future perspective in this feld. Keywords Pollen tube · Embryo sac · Fertilization Introduction During evolution, siphonogamy, a phenomenon depicting the delivery of the immotile sperms to the egg by a pollen tube (PT), emerged in fowering plants. The male gameto- phyte often contains two sperms enclosed in a large veg- etative cell, which germinates the PT to deliver the sperms to the female gametophyte (embryo sac) embedded within the ovule in the ovary for double fertilization. The embryo sac (ES) is a seven-celled structure consisting of an egg, a central cell, two synergids and three antipodal cells (Yang et al. 2010). Upon pollination, pollen land on the stigma and germinate PTs that navigate through the maternal tis- sues to the ovule (Li and Yang 2016). Once it reaches a cer- tain distance from the ovule, the tube is attracted by signals emanated from the ovule to leave the transmitting tract and grows on the funiculus surface toward the ovule. Finally, the embryo sac-secreted attractants guide the tube to the micropyle where it meets and bursts in the synergid of the embryo sac (Takeuchi and Higashiyama 2011; Higashiyama and Takeuchi 2015) (Fig. 1). It is worth to note that only fully developed ES attracts and receives PT in a one-to-one manner. As above, the intimate interplay between the PT and female tissue is critical for sperm delivery. Intercellular crosstalk between the PT and cells of the maternal tissues, and then the ES has been studied extensively during the past two decades (Higashiyama and Yang 2017). In this review, we summarize the key molecules and signaling pathways critical for pollen tube growth in the maternal tissues and pollen tube guidance when approaching the ovule. The sign- aling of self-incompatibility is not within the scope of this review. Communicated by Tetsuya Higashiyama. A contribution to the special issue ‘Plant Reproduction Research in Asia’. * Hong-Ju Li hjli@genetics.ac.cn * Wei-Cai Yang wcyang@genetics.ac.cn 1 State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, East Lincui Road, Beijing 100101, China 2 The University of Chinese Academy of Sciences, 19 Yuquan Road, Beijing 100049, China