Hyperoside promotes pollen tube growth by regulating the depolymerization effect of actin-depolymerizing factor 1 on microfilaments in okra

Biying Dong,Meng Qi,Hongyan Cao,Tingting Du,Qing Yang,Ting Chen,Dong Meng,Zhihua Song,Haojie Jin,Mengying Wang,Yujie Fu,Wanlong Yang,Tengyue Liu,Lili Niu

doi:10.1038/s41438-021-00578-z

Biying Dong, Meng Qi + Show 12 more

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https://doi.org/10.1038/s41438-021-00578-z

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Abstract

Mature pollen germinates rapidly on the stigma, extending its pollen tube to deliver sperm cells to the ovule for fertilization. The success of this process is an important factor that limits output. The flavonoid content increased significantly during pollen germination and pollen tube growth, which suggests it may play an important role in these processes. However, the specific mechanism of this involvement has been little researched. Our previous research found that hyperoside can prolong the flowering period of Abelmoschus esculentus (okra), but its specific mechanism is still unclear. Therefore, in this study, we focused on the effect of hyperoside in regulating the actin-depolymerizing factor (ADF), which further affects the germination and growth of pollen. We found that hyperoside can prolong the effective pollination period of okra by 2–3-fold and promote the growth of pollen tubes in the style. Then, we used Nicotiana benthamiana cells as a research system and found that hyperoside accelerates the depolymerization of intercellular microfilaments. Hyperoside can promote pollen germination and pollen tube elongation in vitro. Moreover, AeADF1 was identified out of all AeADF genes as being highly expressed in pollen tubes in response to hyperoside. In addition, hyperoside promoted AeADF1-mediated microfilament dissipation according to microfilament severing experiments in vitro. In the pollen tube, the gene expression of AeADF1 was reduced to 1/5 by oligonucleotide transfection. The decrease in the expression level of AeADF1 partially reduced the promoting effect of hyperoside on pollen germination and pollen tube growth. This research provides new research directions for flavonoids in reproductive development.

Highlights

In a suitable environment, the pollen on the stigma germinates and grows pollen tubes; the pollen tube extends toward the ovule
We found that AeADF1 is highly expressed in pollen in response to hyperoside and plays a significant role in pollen germination and pollen tube growth by severing actin
The morphology of microfilaments in N. benthamiana cells sprayed with buffer solution only, sprayed with buffer solution containing 0.1 mM hyperoside, and not sprayed with any solution was examined under a laser confocal microscope

Summary

Introduction

The pollen on the stigma germinates and grows pollen tubes; the pollen tube extends toward the ovule. Flavonoids play a significant role in the growth of pollen tubes[2]. By applying specific flavonols to pollen or the stigma during pollination, the defect can be overcome, and fertility can be restored[3,4]. The Arabidopsis CHS mutant (tt4) showed reduced seed setting and reduced pollen germination in vitro[5]. These reports indicate that flavonoids may interfere with pollen germination and pollen tube growth. The specific mechanism by which flavonoids affect pollen germination and pollen tube growth is unclear.

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