Pinning down ploidy in paleopolyploid plants.

Area of Science:

• Evolutionary Biology
• Genomics
• Bioinformatics

Background:

• Whole genome multiplication (WGM) followed by gene fractionation shapes plant evolution over millions of years.
• Analyzing the frequency distribution of gene pair similarities provides evidence for WGM and fractionation processes.
• Repeated cycles of WGM and fractionation are key to understanding plant genome evolution.

Purpose of the Study:

• To model and infer processes of gene fractionation and WGM using gene similarity distributions.
• To develop a birth-and-death model that accounts for multiple WGM events and differential fractionation rates.
• To address questions regarding the number of gene pairs originating from each WGM event.

Main Methods:

• Developed a novel birth-and-death model for WGM and fractionation.
• Incorporated biologically motivated handling of gene survival post-fractionation.
• Applied the model to analyze gene similarity distributions in Brassica rapa.

Main Results:

• The model accurately accounts for the similarity distribution of paralogs resulting from multiple WGM and fractionation rounds.
• Quantitative analysis of high-similarity gene pairs and triples confirmed known ploidy events in B. rapa's evolutionary history.
• The model provides insights into the expected number of gene pairs traceable to specific WGM events.

Conclusions:

• The proposed birth-and-death model effectively explains paralog similarity distributions arising from WGM and fractionation.
• Analysis of gene triples confirms the recent triplication event in the Brassica lineage.
• The study provides a robust framework for studying genome evolution driven by WGM and fractionation.