Cercis: A Non-polyploid Genomic Relic Within the Generally Polyploid Legume Family

Area of Science:

• Evolutionary genomics
• Plant systematics
• Molecular evolution

Background:

• The legume family (Fabaceae) exhibits significant genomic diversity.
• Understanding ancestral legume genomes is crucial for tracing evolutionary pathways.
• The genus Cercis is phylogenetically positioned in an early-diverging lineage within the legume subfamily Cercidoideae.

Purpose of the Study:

• To investigate the evolutionary history of legume genomes using Cercis as a model.
• To reconstruct the ancestral legume chromosome number and genome duplication events.
• To determine the role of polyploidy in the diversification of legume subfamilies.

Main Methods:

• Comparative analysis of genome sequences from diverse legume species.
• Phylogenomic and synteny analyses.
• Analysis of chromosome counts across 477 legume genera.
• Reconstruction of phylogenetic trees and whole-genome duplication histories.

Main Results:

• The Cercis genus genome is small and exhibits a slow mutation rate, suggesting it represents an early evolutionary form.
• Phylogenetic and chromosome count data suggest an ancestral legume progenitor with 7 chromosomes, consistent with Cercis.
• Evidence indicates genome duplication events in other legume subfamilies, likely independent and allopolyploid in origin, while Cercis lacks polyploidy.

Conclusions:

• The genus Cercis serves as a valuable model for understanding early legume genome evolution.
• A 7-chromosome legume progenitor diversified, leading to Cercidoideae and other subfamilies, with Cercis arising from a subsequent Cercidoideae speciation.
• Cercis is unique among investigated legumes for its apparent lack of polyploidy, distinguishing its genomic evolutionary trajectory.