TPJ article: DNA methylation dynamics of sperm cell lineage development in tomato

25 Feb 2021 - By: Leonie Verhage

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DNA methylation dynamics of sperm cell lineage development in tomato

 Lu, Y., Song, Y., Liu, L. and Wang, T.
https://doi.org/10.1111/tpj.15098

 

Pollen development in tomato (Figure by Lingtong Liu)
Pollen development in tomato. The microspore undergoes asymmetrical mitosis (pollen mitosis I) to give rise to a vegetative cell and a generative cell that is enclosed in the cytoplasm of the vegetative cell. The mature pollen grain of tomato is bicellular, and the generative cell divides again (pollen mitosis II) in the pollen tube to produce two sperm cells. Figure by Lingtong Liu.

 

 

In flowering plants, pollen grains are indispensable for sexual reproduction. Pollen develops from single-celled microspores that result from meiosis. First, the microspore divides asymmetrically, resulting in a small generative and a much larger vegetative cell. The vegetative cell exits the cell cycle, but the generative cell divides again to form two sperm cells.

The vegetative cell and the generative cell have different identities and fates. Epigenetic regulation, such as DNA methylation and histone modification, is known to play a fundamental role in controlling cell identity. In issue 105::3 of The Plant Journal, the research group of Tai Wang investigated the role of DNA methylation in the sperm cell lineage by creating a methylome of all three pollen cell types using bisulfite sequencing.

By pairwise comparison of the methylation patterns, they found that there were millions of differentially methylated sites between the microspore and the generative cell, as well as between the microspore and the vegetative cell nucleus. The same was true when they compared methylation in the vegetative cell nucleus to the generative cell. However, there were only 62 differential sites between the generative cell and the sperm cell. Hence, it appears that DNA methylation changes extensively following the asymmetric division but is sustained from the generative cell to the sperm cells. This indicates that sperm cells largely inherit the DNA methylome from the generative cell.

To investigate whether differential methylation correlates with differential expression, the authors identified differentially expressed genes and transposable elements (TEs) and compared these with the differentially methylated regions. As it turned out, most differentially expressed genes and TEs were not differentially marked by methylation. Nevertheless, when they tried to predict gene expression based on methylation level using random forest - a tree-based machine learning tool - they found that methylation in the gene body can be used as a predictor for gene expression. Especially in the microspore, they found a negative correlation between gene body methylation and gene expression. Hence, methylation appears to reflect gene expression in the sperm cell lineage, at least to some extent.

As it appears, tomato sperm cells are helped in finding their identity by copying the methylation patterns of the parent cell.

Leonie Verhage, Research Highlights Editor


Author: Leonie Verhage
Category: The Plant Journal
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Leonie Verhage

Leonie Verhage

Leonie Verhage is Research Highlights Editor at The Plant Journal. For every issue, she highlights one of the key articles with a commentary paper.
On Twitter, Leonie keeps the followers of The Plant Journal (@ThePlantJournal) updated on the latest articles.