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Live-cell imaging reveals the dynamics of two sperm cells during double fertilization in Arabidopsis thaliana |
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| Authors: | Hamamura Yuki Saito Chieko Awai Chie Kurihara Daisuke Miyawaki Atsushi Nakagawa Tsuyoshi Kanaoka Masahiro M Sasaki Narie Nakano Akihiko Berger Frédéric Higashiyama Tetsuya |
| Institution: | 1 Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan 2 JST ERATO Higashiyama Live-Holonics Project, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan 3 Molecular Membrane Biology Laboratory, Advanced Science Institute, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan 4 Laboratory for Cell Function and Dynamics, Brain Science Institute, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan 5 Research Institute of Molecular Genetics, Shimane University, Matsue, Shimane 690-8504, Japan 6 Department of Biological Sciences, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan 7 Temasek Life Sciences Laboratory, 1 Research Link, National University of Singapore, 117604 Singapore 8 Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, 117543 Singapore |
| Abstract: | Flowering plants have evolved a unique reproductive process called double fertilization, whereby two dimorphic female gametes are fertilized by two immotile sperm cells conveyed by the pollen tube. The two sperm cells are arranged in tandem with a leading pollen tube nucleus to form the male germ unit and are placed under the same genetic controls. Genes controlling double fertilization have been identified, but whether each sperm cell is able to fertilize either female gamete is still unclear. The dynamics of individual sperm cells after their release in the female tissue remain largely unknown. In this study, we photolabeled individual isomorphic sperm cells before their release and analyzed their fate during double fertilization in Arabidopsis thaliana. We found that sperm delivery was composed of three steps. Sperm cells were projected together to the boundary between the two female gametes. After a long period of immobility, each sperm cell fused with either female gamete in no particular order, and no preference was observed for either female gamete. Our results suggest that the two sperm cells at the front and back of the male germ unit are functionally equivalent and suggest unexpected cell-cell communications required for sperm cells to coordinate double fertilization of the two female gametes. |
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