Scientists decode vesicle-mediated growth in pollen tubes of wishbone flower
image: Schematic diagram of TfANX- and TfRABA4D-mediated pollen tube integrity and tip growth in T. fournieri. (A) TfANX regulates pollen tube integrity in a ROS-independent way, leading to the leakage in developing pollen tubes, distinct from rupture for sperm cell release in the mature pollen tube. (B) TfRABA4D supports tip growth by coordinating pectin deposition, vesicle distribution, and ROS accumulation, preventing abnormal swelling at the tip.
Credit: Horticulture Research
Fertilization in flowering plants relies on the fast-growing pollen tube, a cellular conduit that delivers sperm cells to the ovule. This study sheds light on the vesicle trafficking mechanisms that sustain pollen tube tip growth and fertility. Using the wishbone flower (Torenia fournieri) as a model, researchers combined the chemical inhibitor brefeldin A (BFA) with antisense oligodeoxynucleotides (AS-ODNs) to disrupt vesicle activity and suppress specific genes. The inhibition altered cell wall formation, vesicle distribution, and reactive oxygen species (ROS) accumulation, ultimately distorting pollen tube morphology. The findings provide a new strategy to study gene function in reproductive tissues of non-model plants.
Pollen tube growth is one of the most dynamic examples of plant cell elongation, relying on vesicle-mediated trafficking to deliver cell wall materials and maintain polarity. In model plants like Arabidopsis and tobacco, genes regulating vesicle transport have been identified, but stable transformation systems are often lacking in ornamental or non-model species. The absence of genetic tools limits the study of reproductive processes in such plants. Chemical inhibitors and transient gene suppression approaches offer fast and reversible alternatives to reveal gene function. Due to these challenges, a deeper investigation into vesicle trafficking mechanisms in non-model pollen tubes is urgently needed.
Researchers from the University of Tokyo reported on January 15, 2025, in Horticulture Research that they have successfully combined brefeldin A (BFA) treatment and antisense oligodeoxynucleotide (AS-ODN) technology to investigate vesicle trafficking in the pollen tubes of Torenia fournieri. Their work (DOI: 10.1093/hr/uhaf018) demonstrates how vesicle activity influences cell wall composition, reactive oxygen species (ROS) localization, and pollen tube integrity. This study establishes a new experimental platform for gene function analysis in non-transgenic systems and expands reproductive biology research to species beyond traditional model plants.
The team found that BFA disrupted vesicle gradients at the pollen tube tip, resulting in reduced germination rates and bulbous tube morphology. Fluorescent imaging showed that secretory vesicles, normally concentrated in the apical region, became dispersed, forming “BFA compartments.” This disturbance also altered the distribution of pectin and callose within the cell wall and decreased tip-localized ROS levels.
To validate gene-specific functions, researchers used antisense oligodeoxynucleotides (AS-ODNs) targeting TfANX, a pollen receptor kinase, and TfRABA4D, a Rab GTPase regulating vesicle trafficking. Silencing TfANX caused abnormal leakage at multiple tube sites, revealing its essential role in maintaining structural integrity. Suppressing TfRABA4D mimicked BFA effects, producing swollen tubes, disrupted pectin gradients, and reduced ROS accumulation. These results confirm that vesicle trafficking coordinates wall deposition and redox balance required for directional growth. Importantly, AS-ODNs successfully penetrated the pollen tubes in a vesicle-dependent manner, offering a reliable method for transient gene inhibition in Torenia.
“Our findings reveal that vesicle trafficking not only supplies cell wall materials but also orchestrates redox signaling essential for pollen tube elongation,” said Professor Tetsuya Higashiyama, corresponding author of the study. “By combining chemical and molecular approaches, we were able to dissect key pathways in a plant species that previously lacked genetic tools. This opens the door to functional studies of reproduction in many horticultural plants that are otherwise difficult to manipulate at the genetic level.”
This study provides an innovative framework for analyzing pollen tube dynamics and gene functions without relying on stable transformation. The AS-ODN–based approach can be adapted to other non-model flowering plants, enabling rapid exploration of genes involved in reproduction, growth, and fertility. Beyond advancing fundamental plant cell biology, understanding vesicle trafficking offers potential applications in improving crop breeding and fertility control. By uncovering how vesicles regulate pollen tube integrity and fertilization success, researchers pave the way for future innovations in plant reproductive biotechnology and high-efficiency hybrid crop development.
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References
DOI
Original Source URL
https://doi.org/10.1093/hr/uhaf018
Funding information
The authors gratefully acknowledge financial support from the MEXT Scholarship with Embassy Recommendation via the China Scholarship Council to X.J. This work was also supported by grants from the Japan Society for the Promotion of Science (21K15119 to A.G.M., 22H05172, 22H05178 to S.O., and 21K18235, 22H04980, 22K21352 to T.H.) and the Japan Science and Technology Agency (JPMJCR20E5 to T.H.).
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.