The Physcomitrella patens chromosome-scale assembly reveals moss genome structure and evolution

Area of Science:

• Genomics
• Plant Biology
• Evolutionary Biology

Background:

• The draft genome of the moss model Physcomitrella patens was previously composed of approximately 2000 unordered scaffolds.
• Understanding genome structure and evolution is crucial for comparative plant biology.

Purpose of the Study:

• To generate a chromosome-scale genome assembly for Physcomitrella patens.
• To analyze the genome structure, evolution, and unique features of this moss model.

Main Methods:

• Genetic linkage mapping was employed.
• End sequencing of long DNA fragments was utilized.
• Structure-based detection methods were used to identify whole genome duplications.

Main Results:

• A chromosome-scale assembly was generated, revealing 57% transposable elements (TEs) with even distribution.
• Unlike flowering plants, Physcomitrella patens chromosomes are mono-centric, with TEs potentially near centromeres.
• Gene body methylation was observed in 5.7% of genes, associated with low GC and expression.
• Giant virus insertions are transcriptionally active and may confer viral resistance.
• The genome shows evidence of two whole genome duplication (WGD) events, common in mosses.
• Conserved syntenic regions suggest ancient gene functions related to plant growth and organization.
• Physcomitrella patens lacks typical TE-rich pericentromeric and gene-rich distal regions found in flowering plants.

Conclusions:

• The Physcomitrella patens genome exhibits a unique structure compared to flowering plants, characterized by even TE distribution and mono-centric chromosomes.
• Whole genome duplications played a significant role in moss genome evolution.
• Further non-seed plant genome studies are needed to determine if this structure is typical for mosses or bryophytes and to understand broader plant genome evolution.