Pollen navigation
Multiple fertilizations of an ovule do not contribute to healthy offspring. Plants therefore have taken measures to prevent this. Now researchers from Japan show how a plant manages this.
The landing of a pollen grain on a pistil of a flower is only the first hurdle of fertilization. After landing the pollen grain initiates the growth of a pollen tube that brings the pollen grain to the ovule. During this process the pollen tube gets instructions from the ovule. The Japanese researchers decided to study this process in more detail.
They did this through detailed recording of the pollen tube. Through this the researchers discovered what influenced the choice for a specific ovule. This was not as expected the landing place on the pistil. A pollen tube is not actually growing straight downwards, but more in a kind of zigzaggedly way. As soon as such a zigzagging pollen tubes came near an ovule, it slowed its growth. Subsequently the pollen tube grew more directly towards the ovule.
The ovule sends out at least three signals that the pollen tube can navigate by
That this is precisely regulated came clear when the researchers analysed some plants missing essential fertilization genes. By those it goes wrong and can the pollen tube not find the ovule. The ovules are therefore sending a signal: Here am I. Although it is not yet clear how this signal exactly looks like.
The next thing the researchers checks was if there was a signal that prevents multiple fertilisation events. They noticed that by mother plants without FERONIA the ovules often were fertilised multiple times. Suggesting that FERONIA sends out a signal: stop, I am already fertilised.
The researchers think that the ovule actually sends this signal just before it is actually fertilised. So that it is slowing down the competition. But not yet excluding a second fertilisation. This it turned out to be the case only 45 minutes after fertilisation.
So researchers need to hunt for three signals. One that says: Here am I. One that tells that there is already a suiter. And one that say: I am fertilised. Together these three signals for the navigation system for the pollen tube.
Literature
Yoko Mizuta, Daigo Sakakibara, Shiori Nagahara, Ikuma Kaneshiro, Takuya T Nagae, Daisuke Kurihara, and Tetsuya Higashiyama (2024) Deep imaging reveals dynamics and signaling in one-to-one pollen tube guidance, EMBO reports https://doi.org/10.1038/s44319-024-00151-4
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