Using plastid genome-scale data to resolve enigmatic relationships among basal angiosperms

Area of Science:

• * Plant evolutionary biology
• * Molecular phylogenetics
• * Angiosperm genomics

Background:

• * The evolutionary relationships among early flowering plant lineages (angiosperms) remain challenging to resolve.
• * The branching order of the five major mesangiosperm clades (Ceratophyllum, Chloranthaceae, eudicots, magnoliids, and monocots) is particularly debated.
• * Previous phylogenetic analyses have lacked consistent support for these basal relationships.

Purpose of the Study:

• * To resolve the phylogenetic relationships among the five major mesangiosperm clades.
• * To investigate the rapid diversification event in early angiosperm evolution.
• * To provide the complete plastid genome sequence for Ceratophyllum demersum.

Main Methods:

• * Phylogenetic analyses were conducted using 61 plastid genes (approximately 42,000 bp) from 45 diverse angiosperm taxa.
• * Maximum-likelihood (ML) and parsimony methods were employed for phylogenetic inference.
• * The complete plastid genome sequence of Ceratophyllum demersum was generated and analyzed.

Main Results:

• * Maximum-likelihood analyses provided more stable phylogenetic topologies compared to parsimony analyses.
• * Total evidence ML analyses strongly supported a clade comprising Chloranthaceae + magnoliids sister to a clade of monocots + (Ceratophyllum + eudicots).
• * High bootstrap and Bayesian support values were observed for these relationships, though some alternative topologies could not be rejected.

Conclusions:

• * The study proposes a new, well-supported phylogenetic framework for basal angiosperm relationships.
• * Evidence suggests a rapid diversification event among these early lineages, occurring approximately 140-144 million years ago.
• * The findings contribute significantly to understanding the early evolution and diversification of flowering plants.