A research team led by Professor Zhang Yan from the College of Life Sciences at Nankai University has recently achieved a major breakthrough in plant reproductive biology. The study revealed a key mechanism governing polarity establishment during pollen germination. The research, titled “Rab5 GTPases mediate the targeting of ROP signaling to establish polarity for pollen germination”, was published in the leading international journal Nature Plants.

Pollen germination is the critical first step in the reproduction of flowering plants. Much like a seed sprouting, the pollen grain must determine the precise direction to extend a pollen tube. How this initial symmetry-breaking event occurs—transforming a non-polar cell into a polar one—has long remained a fundamental mystery in plant reproductive biology. This study focused on the core signaling molecules regulating this process: ROP GTPases. The research team, led by Professor Zhang Yan, has identified Rab5 GTPases as the key navigators in this process. In a groundbreaking discovery, the study demonstrates that non-polarly localized Rab5 proteins recruit the ROP activator RopGEF8 through direct physical interaction. This mechanism ensures the precise delivery of signaling molecules to specific sites on the pollen cell membrane, thereby triggering the polarity establishment required for germination.

Working model: Rab5 GTPase-mediated regulation of ROP signaling ensures pollen germination

Importantly, the study also unveils a sophisticated redundant backup system in Arabidopsis thaliana. By utilizing two types of Rab5 proteins—evolutionarily conserved and plant-specific—plants ensure robust pollen germination even if one pathway is compromised. This work not only deciphers the unique regulatory strategy plants use to spatially target ROP signaling, but also provides a novel paradigm for how symmetry-breaking and spatial information arise from a non-polar state—findings that hold significant implications for plant fertilization and reproductive isolation.

Dr. Hao Guangjiu from College of Life Sciences at Nankai University and doctoral student Yu Fei from Shandong Agricultural University are the co-first authors of this study, with Professor Zhang Yan and Professor Li Xia serving as co-corresponding authors. Dr. Liang Zizhen from the Chinese University of Hong Kong also contributed to the research. Beyond its fundamental discoveries, this work holds profound theoretical importance for understanding plant fertilization, crop male sterility, and the mechanisms of reproductive isolation.

Link to the paper: https://doi.org/10.1038/s41477-025-02130-6

（Edited and translated by Nankai News Team.)