How evolution repeatedly builds complexity: a case study with C₄ photosynthesis in Blepharis (Acanthaceae).

Area of Science:

• Plant Biology
• Evolutionary Biology
• Biochemistry

Background:

• C4 photosynthesis has evolved over 60 times, making it ideal for studying complex trait evolution.
• Limited availability of C3-C4 intermediate species hinders understanding of C4 evolution models.
• The genus Blepharis presents an opportunity to study C3-C4 transitions due to its diverse species.

Purpose of the Study:

• To characterize the phenotypic diversity of C3-C4 photosynthesis in Blepharis.
• To investigate the evolutionary pathways and origins of C4 photosynthesis within Blepharis.
• To establish Blepharis as a model system for studying the convergent evolution of complex traits.

Main Methods:

• Phenotypic characterization of 28 Blepharis species (photosynthetic gas exchange, enzyme activity, cell ultrastructure, δ13C).
• Analysis of 92 herbarium specimens for δ13C isotopic signatures.
• Phylogenetic analysis using transcriptome data to reconstruct evolutionary history.

Main Results:

• Identification of C3, proto-Kranz, C2, C4-like, and C4 phenotypes within Blepharis sect. Acanthodium.
• Phylogenetic evidence supports a stepwise C3 to C4 progression with up to five independent C4 origins.
• Significant intraspecific variation in C2-C4 states observed in B. mitrata, B. furcata, and B. macra.
• Blepharis gazensis exhibits a unique NADP-ME C4 pathway, expanding known C4 functional diversity.

Conclusions:

• Blepharis harbors substantial photosynthetic diversity, comparable to other C3-C4 transitional lineages.
• The genus provides a robust model for studying the convergent evolution of C4 photosynthesis and complex traits.
• Stepwise evolution and multiple origins of C4 photosynthesis are supported within Blepharis.