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MpMLO1 controls sperm discharge in liverwort
Meng-Xing Cao1,2, Shi-Zhen Li1,2, Hong-Ju Li3,4,5
1Key Laboratory of Seed Innovation, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China.
Abstract:
In bryophytes, sexual reproduction necessitates the release of motile sperm cells from a gametophyte into the environment. Since 1856, this process, particularly in liverworts, has been known to depend on water. However, the molecular mechanism underlying this phenomenon has remained elusive. Here we identify the plasma membrane protein MpMLO1 in Marchantia polymorpha, a model liverwort, as critical for sperm discharge from antheridia. The MpMLO1-expressing tip cells among the sperm-wrapping jacket cells undergo programmed cell death upon antheridium maturation to facilitate sperm discharge after the application of water and even hypertonic solutions. The absence of MpMLO1 leads to reduced cytoplasmic Ca2+ levels in tip cells, preventing cell death and consequently sperm discharge. Our findings reveal that MpMLO1-mediated programmed cell death in antheridial tip cells, regulated by cytosolic Ca2+ dynamics, is essential for sperm release, elucidating a key mechanism in bryophyte sexual reproduction and providing insights into terrestrial plant evolution.
Insights
A newly identified protein, MpMLO1, is crucial for sperm release in liverworts. It triggers programmed cell death in antheridial tip cells, enabling sperm discharge and aiding plant evolution.
Area of Science:
- Plant Reproduction
- Bryophyte Biology
- Molecular Mechanisms
Background:
- Bryophyte sexual reproduction requires motile sperm release from gametophytes.
- Water dependency for sperm release in liverworts is known since 1856, but molecular mechanisms were unclear.
Purpose of the Study:
- To identify the molecular factors controlling sperm discharge in the model liverwort Marchia polymorpha.
- To elucidate the mechanism of water-dependent sperm release.
Main Methods:
- Identification of MpMLO1 as a key plasma membrane protein in Marchia polymorpha.
- Analysis of MpMLO1 function in antheridial tip cells and its role in programmed cell death.
- Investigation of cytosolic Ca2+ dynamics in relation to MpMLO1 activity.
Main Results:
- MpMLO1 is essential for sperm discharge from antheridia.
- MpMLO1 triggers programmed cell death in antheridial tip cells, facilitating sperm release.
- Absence of MpMLO1 reduces Ca2+ levels, inhibits cell death, and prevents sperm discharge.
Conclusions:
- MpMLO1-mediated programmed cell death in antheridial tip cells is vital for sperm release in bryophytes.
- Cytosolic Ca2+ dynamics regulate this process, essential for sexual reproduction.
- Findings offer insights into early terrestrial plant evolution.
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