Researchers found that attractant peptides released by female tissues initiate rapid depolymerization and repolymerization of actin at the leading edge of the pollen tube tip, steering its direction before visible changes occur. This cytoskeletal restructuring is essential for the successful redirection of the pollen tube.
Fertilization in flowering plants hinges on the accurate guidance of pollen tubes, which deliver sperm cells to the ovule. Pollen tubes serve as delivery systems for immotile sperm cells, enabling double fertilization. These tubes grow rapidly and must constantly change direction in response to female-derived attractant peptides, such as AtLURE1s, to reach the ovule. Previous studies have identified key receptor-like kinases and signaling peptides involved in this guidance system, but the downstream cellular mechanisms have remained unclear. Actin filaments, known to support tip growth via vesicle trafficking, were suspected to play a role. However, their exact contribution to signal-induced turning had not been directly visualized.
A study (DOI: 10.48130/seedbio-0024-0014) published in Seed Biology on 12 September 2024 by Shanjin Huang’s team, Tsinghua University, highlights the key role of actin-depolymerizing factor ADF10 in this process, establishing a vital link between signaling cues and cytoskeletal dynamics.
To investigate the cellular mechanisms behind pollen tube turning in response to female attractant signals, researchers employed a semi-in vitro assay responsive to the peptide AtLURE1.2. This setup allowed for direct visualization of actin filament dynamics within pollen tubes using live-cell imaging techniques. Initial medium optimization identified 3#PGM as the most effective for supporting pollen tube growth. Under AtLURE1.2 stimulation, wild-type (WT) pollen tubes exhibited wavy growth patterns, while mutant prk6 tubes maintained straight growth, confirming a specific response to the peptide. Fluorescently tagged actin markers (Lifeact-EGFP and FIM5-EGFP) revealed that, during AtLURE1.2-induced turning, actin filaments at the pollen tube's leading side rapidly depolymerized and then repolymerized, reconstructing the apical actin structure prior to morphological changes. This dynamic remodeling was absent at the tube’s rear side. To probe the regulatory role of actin-depolymerizing factor ADF10, mutant lines (adf10-1 and adf10-2) were analyzed. These mutants, though attracted to AtLURE1.2 beads, displayed irregular and reduced-amplitude turning, along with impaired actin filament depolymerization and persistent accumulation of disorganized filaments at the turning site. Further imaging showed that ADF10 accumulates asymmetrically at the subapical leading edge before turning and redistributes symmetrically post-turn. These results demonstrate that ADF10-driven actin depolymerization is an early and essential event for reorganizing the apical cytoskeleton, enabling directional pollen tube growth in response to external guidance cues.
Understanding the cellular mechanics of pollen tube guidance opens new avenues in plant breeding and crop improvement. By manipulating the signaling or actin regulatory pathways, it may be possible to enhance fertilization efficiency, particularly in crops with reproductive barriers or under environmental stress. Moreover, the principles uncovered in this study could inform synthetic biology approaches aimed at engineering directional growth in plant or fungal systems.
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References
DOI
10.48130/seedbio-0024-0014
Original Source URL
https://doi.org/10.48130/seedbio-0024-0014
Funding information
This study was supported by a grant from the National Natural Science Foundation of China (32270338).
About Seed Biology
Seed Biology (e-ISSN 2834-5495) is published by Maximum Academic Press in partnership with Yazhou Bay Seed Laboratory. Seed Biology is an open access, online-only journal focusing on research related to all aspects of the biology of seeds, including but not limited to: evolution of seeds; developmental processes including sporogenesis and gametogenesis, pollination and fertilization; apomixis and artificial seed technologies; regulation and manipulation of seed yield; nutrition and health-related quality of the endosperm, cotyledons, and the seed coat; seed dormancy and germination; seed interactions with the biotic and abiotic environment; and roles of seeds in fruit development. Seed biology publishes a wide range of research approaches, such as omics, genetics, biotechnology, genome editing, cellular and molecular biology, physiology, and environmental biology. Seed Biology publishes high-quality original research, reviews, perspectives, and opinions in open access mode, promoting fast submission, review, and dissemination freely to the global research community.