Wang Yingxiang's team at Fudan University revealed the molecular mechanism of gene silencing in meiosis recombinant hot zones

Wang Yingxiang's team at Fudan University revealed the molecular mechanism of gene silencing in meiosis recombinant hot zones

Merosis is a special way of cell division necessary for eukaryotic sexual reproduction, which eventually produces haploid gametes
.
Meiosis recombination is a core event of meiosis that begins with the generation
of DNA double-stranded breaks (DSB) mediated by the conserved DNA topoisomerase complex (SPO11-1/SPO11-2/MTOPVIB).
In addition to creating new allelic combinations, meiosis homologous chromosome recombination not only ensures the stable transmission of genetic material between generations, but also increases the genetic diversity
of offspring.
In yeast, mammal, and plant studies, it has been found that the distribution of meiosis DSB along chromosomes is not random, but preferentially occurs in small areas (~1-2 kb), known as DSB hot zones, which have significant epigenetic modifications and genomic characteristics
.
Histone modifications such as H3K4me3, H3K36me3, histone variant H2A.
Z, etc.
were found in plants to be enriched
in hot zones.
Both germinating yeast and plants suggest that DSB predispositions occur at the transcriptional initiation site (TSS) of genes, accompanied by low nucleosome density, suggesting that DSB typically occurs in chromosome open regions
with transcriptionally active characteristics.
Interestingly, gene transcription and DNA repair at DSB sites are inversely correlated, while gene transcription status and its regulatory mechanisms at DSB sites during plant meiosis have not been reported
.

Figure 1.
POL ε-SUVH2/9 model for gene silencing that regulates meiosis DSB conjugation

On October 3, 2022, Wang Yingxiang's research group published a research paper entitled "DNA polymerase epsilon interacts with SUVH2/9 to repress the expression of genes associated with meiotic DSB hotspot in Arabidopsis" on PNAS
。 The study revealed the molecular mechanism of gene silencing at the DNA double-stranded break (DSB) site during plant meiosis, revealing new functions
of the DNA polymerase epsilon (POL ε) and SUVH2/9 in meiosis cells that differ from those in somatic cells.

In the previous work, researchers found that different DNA polymerases (Pol α, Pol δ and Pol ε) play a role in meiosis recombinant DNA repair, in which the catalytic subunit POL2A of Pol ε is crucial for the repair and recombinant distribution regulation of meiosis DSB (Huang et al.
, PNAS, 2015).

Then, as the cells move on to further exploration, the DNA polymerase will still be distributed across the chromosome, and this study reports its function
in the autochromatin DSB-enriched region.
The researchers found that the component SUVH2 interacts with
POL2A and RdDM (RNA-directed DNA methylation).
Further studies verified the interaction between the N-terminal of POL2A and the SET domain of SUVH2/9, and using N-SIM (Structured Illumination Microscopy), it was observed that SUVH2 co-localized with γ-H2AX-tagged DSB during meiosis and that this localization was dependent on POL2A
.
It is implied that POL2A recruits SUVH2
during meiosis DSB repair.

SUVH2 and its homologous protein SUVH9 in the RdDM pathway affect the production of small RNAs at target sites and methylation
of CHH (H for A, T, or G).
Through high-throughput sequencing, the researchers found that unlike SUVH2/9 in inhibiting TE expression in somatic cells, SUVH2/9 and POL2A together inhibited the expression
of 865 genes in meiosis cells.
And these 865 genes are not directly involved in regulating meiosis function, but have significant characteristics of DSB thermal regions in their transcriptional initiation site (TSS) region, including low nucleosome density, A-rich motifs, and enrichment of SPO11-1
.
This result suggests that POL2A and SUVH2/9 may play a role
in gene silencing at the meiosis DSB location.
At the same time, the researchers found that this function is not similar to that achieved in somatic cells by regulating the methylation or small RNA of DNA, but both POL2A and SUVH2/9 affect the concentration of meiosis chromosomes, suggesting that they may inhibit gene expression directly by regulating chromatin structure (Figure 1).

Finally, through genetic analysis, the researchers also found that the mutation of SUVH2/9 further strengthens the meiosis DSB repair of POL2A mutants and the phenotype
of male sterilization.
And the more genes that are usually upregulated in each mutant, the more defects accompanied by meiosis DSB repair abnormalities
.
Therefore, we speculate that gene silencing induced by POL2A and SUVH2/9 at the DSB site is of great significance
for normal meiosis DSB repair.

Figure 1.
POL ε-SUVH2/9 model for gene silencing that regulates meiosis DSB conjugation

In summary, the study revealed the transcriptional state of genes at plant DSB locations and discovered a novel mechanism by which the DNA polymerase epsilon and SUVH2/9 jointly regulate transcriptional silencing of meiosis DSB coupling (Figure 1), which may be critical
for DSB repair and genome stability of the meiosis process.

Dr.
Cong Wang, a postdoctoral fellow of Professor Yingxiang Wang, School of Life Sciences, Fudan University, is the first author of the paper, and his doctoral and postdoctoral fellows have published 5 papers
in PNAS (2), Plant Cell (1) and Plant Physiology (2) with the first (including the joint).
Professor Wang Yingxiang and Young Researcher You Chenjiang are co-corresponding authors
.
Professor Gregory Copenhaver of the University of North Carolina at Chapel Hill, Professor Huang Jiyue of South China Agricultural University, and doctoral students Zhang Jun and Yu Yue of Fudan University also participated in the work
.
The work has been funded
by the National Natural Science Foundation of China, Fudan University, the China Postdoctoral Fund and the University of North Carolina.

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