The Chara Genome: Secondary Complexity and Implications for Plant Terrestrialization

Area of Science:

• * Evolutionary biology
• * Genomics
• * Phycology

Background:

• * Land plants (embryophytes) evolved from freshwater green algae.
• * Charophyceae algae, particularly Chara species, exhibit complex body plans and are considered the closest living relatives to land plants.
• * Understanding the Chara genome is crucial for identifying genetic innovations enabling plant terrestrialization.

Purpose of the Study:

• * To present the genome sequence of Chara braunii.
• * To compare the Chara braunii genome with land plant genomes to identify evolutionary novelties and shared heritage genes.
• * To investigate the genetic basis of Chara braunii's morphological complexity and reproductive strategies.

Main Methods:

• * Whole-genome sequencing and comparative genomics.
• * Analysis of gene families, including those involved in cell wall biosynthesis, signaling, and stress tolerance.
• * Transcriptomic analysis of sexual reproductive structures.

Main Results:

• * Chara braunii possesses unique xylan synthases for cell wall biosynthesis and a phragmoplast mechanism similar to land plants.
• * Land-plant-like retrograde signaling controls Chara braunii plastids, with more elaborate transcriptional regulation than other algae.
• * Expanded gene families related to reactive oxygen species (ROS) tolerance, LysM receptor-like kinases, and transcription factors (TFs) are linked to morphological complexity.
• * Transcriptomic data reveal intricate TF control, ROS gene network activity, and ancestral plant-like proteins in zygotes.

Conclusions:

• * The Chara braunii genome provides insights into the genetic toolkit required for plant terrestrialization.
• * This organism exhibits a mix of algal and land-plant-like features, highlighting key evolutionary transitions.
• * Complex morphological and reproductive traits in Chara braunii are underpinned by expanded gene families and intricate regulatory networks.